Torque, HP and Thrust tests


Here is a look at a classic testing story from our days at the Edgewater Florida hangar . The years we spent there (2004-2008), maked the sucessful completion of many planes and hosting a number of outstanding colleges. The pace of testing was going into high gear then. The story notes that we had previously run 50 engines on the run stand before it was converted to a dyno. In the years that followed, we ran more than 100 engines on the dyno, most of the in public or at college where we invited people to study the system and verify the conclusions.

Today, the run stand we use at the college is made from many of the same parts we used on the dyno. It has been simplified to allow much faster engine changes required to run many engines at a college. If you look at the engines in all the tests, you can see that they are all 2700s that pre-date any of our Gold system components. (Gold oil systems eleminate the need to verify the stock oil bypass as shown in the story) The engines we build today, the 2,850s and 3,000cc power plants, are even more powerful than the engines in the tests, with no sacrifice in reliability. As we have extracted more power, we have done it largely by increasing the displacement of the engine, so the power output per cubic inch has stayed about the same, keeping the stress on the engine to very conservative levels.

Torque, Horsepower and Thrust Testing

September 21, 2004


Here’s the second engine being run on our dynamometer. We ran this a few hours ago. In the photo above, Gus is checking the timing with a light. We spent some time this week upgrading the dynamometer in its details. Visible is its new paint job, but it got a lot of detail work to facilitate rapid engine changes, and multiple tests. I contacted Darryl at Warp Drive Propellers today, and he’s sending us down a matched set of smaller diameter blades which will allow us to graph the horsepower at high rpm settings. These blades will become part of the permanent setup. The engine shown here in the test is a virtual clone of our 601 engine. The only significant difference is that this engine has GM steel rockers, while our 601 engine has roller rockers. I built this engine to represent our standard engine configuration, and use it as a test engine for the dynamometer. It’s fully airworthy and has many nice details like ARP close tolerance through case studs. After the break in and dyno runs, this engine will be for sale.

Here’s a side view of the same engine running, above. This engine has the inward leaning, welded on aluminum intake tubes that fit in our 601 Nosebowl. The intake manifold has four rubber slip joints in it that allow it to mate to many different intake pipe configurations. In photos below, you’ll see the PC Cruiser engine, which has a different intake pipe configuration. The adjustable intake manifold for the dynamometer quickly mated to both motors with a minimum of fuss. These types of details will allow many engines to be evaluated on the dyno. There are 5/8″ and 3/8″ tubes welded into the left valve cover. These mate up to the readily available and highly effective air/oil separator sold by Wick’s and Spruce. The gauge measures mechanical oil pressure. Temperature and rpm are measured remotely. We’ve painted the heavy duty baffle box green. The exhaust system is currently stock iron manifolds with 1 1/2″ down tubes. Shortly, we’ll have mufflers in place.

Above is the front and right side of the engine. The right valve cover has the oil filler neck welded in at the back. The starter motor is the Ultra Low Profile configuration, which fits inside the 601 Nosebowl. The alternator is not yet mounted, but the corner of the front alternator bracket is visible at the edge of the Ring Gear. The Pulley to drive the front alternator is just ahead of the Ring Gear. Pushrod tubes on all of our production engines have always been painted white. While many people believe that oil returning to the crankcase through the pushrod tubes is cooled by airflow through the motor, our testing has shown that just the reverse is true; the pushrod tubes run significantly hotter than the oil in the sump. We paint the tubes white to help them reflect heat.

The photo above shows a very important piece of test equipment that we use on all the motors we build. We use this to evaluate the condition of the oil cooler bypass in the engine. The cooler bypass performs a crucial function in the Corvair. It has a tradition of trouble free operation, even in engines 30 years old. The Corvair’s oil system has a very good track record, and the design of the cooler bypass contributes to this. However, in the interest of truly knowing its condition, we built this tool. The bypass is a pressure sensitive check valve set to relieve at 7 to 8 psi differential. When operating correctly, it allows the motor to warm up the oil quickly. But if it leaks or has a weak spring, the engine will have hot oil temperatures no matter how big a cooler you put on it. This tool, made from a modified oil cooler mount, bolts on to the stock cooler mount and allows me to measure the exact pressure at which the bypass relieves. This is done when the oil pump is being primed with a drill motor, long before the engine is ever run.

Above is the cooler bypass tool in action. Although the photo is a bit blurry, you can see an 8psi differential on the two gauges. The engine is sitting on the dyno being dressed out. What’s driving the oil pressure is a half inch electric drill using a dummy distributor housing and distributor shaft without a drive gear on it. You’ll see this priming tool in many photos. It’s painted orange like many of our shop tools. I primed this motor for 20 minutes with the drill turning the pump at a speed that would be comparable to a high idle on the engine. During this time, I turned the propeller over slowly by hand a bunch of times, allowing the oil to flow through all the passages in the engine. This technique is very effective. This motor has Sealed Power hydraulic lifters, and these, combined with priming, did not let out a single tick when we started the engine an hour later. These hydraulic lifters will maintain their adjustment for the life of the motor. It’s attention to detail like this that pays rewards no matter what type of engine you’re building.

Stay tuned for the test data and horsepower calculations. We’re going to run this motor for a few more hours before we give it full power runs on the dyno.

Thank you.

William Wynne

September 9, 2004


Here is the first run on our newly built engine dynamometer. There are many types of engine dynamometers. One of the most simple and easily made measures the engine’s torque reaction. Our own stand has a motor mount which is free to pivot along the crankshaft axis. This is restrained from rotating by a hydraulic cylinder. It is a simple calculation verified by a simple test, and you can ascertain the amount of torque the engine is producing at any given instant by reading the hydraulic pressure. It is accurate, and if you have the capability of measuring the rpm of the engine very accurately at the same moment, a simple calculation will give you the exact horsepower that the engine is producing. Shown above is the very first run we did on the dynamometer. Its details are still being finished, but it works very well.

Above is the view of the dynamometer with the engine removed. Its operation is very simple. Everything seen in blue rotates on the crankshaft’s axis. If you look closely, you can see that the bearing is the front spindle, hub and wheel removed from a late model Corvair. The bed type mount is slung low so that the crankshaft centerline lines up exactly with the spindle. The reinforcements below the engine contact a bearing at the bottom of the stand for additional support. This is a Corvair blower bearing rolling sideways on a steel plate. It effectively has no drag. Below the spindle is the mounting point for the hydraulic cylinder. The green oxygen bottle has been converted to a gravity feed fuel tank on the test stand. It hold 2.5 gallons of fuel, and has a very accurate sight gauge on it which allows precision measurement of fuel burn.

Another view of the first run is above. Just ahead and above the battery is the hydraulic cylinder. A stainless braided line running out of the picture goes to the remote gauge. Our rpm measurement is by digital optical tachometer. This is one of the few types of tachs accurate enough to give good test information. Many people will recognize the chassis of the dynamometer as our previous engine run stand. The old stand served us well, and broke in many famous Corvair engines, such as Mark Langford’s 3100. Although we never kept count, I’m pretty sure 50+ engines were run on it. The new dynamometer is capable of everything that the old run stand could do, plus its obvious new function of measuring horsepower. In the coming year, we’d like to run as many engines as possible and anyone converting a Corvair for flight reading this is certainly welcome to bring their engine for a run. We took the time to manufacture a very special intake manifold for the dynamometer which is compatible with any style of cylinder head used in Corvair flight motors. Details like this will make installing and running engines a quick and simple process.

Gus monitors the engine run, above. Note the newly constructed heavy duty baffle box to provide cooling air to test engines. I’ve said it many times, but it’s worth repeating that you should not run your motor even briefly without a cooling system in place. The carburetor in this run is an MA3-SPA from an O-200. This will be the dedicated carburetor on the dynamometer, although we will be able to evaluate others. The propeller is a 72″ 2-blade Warp Drive. In the background in this photo is the Corvair Trimotor fuselage.

Above is another view of the running engine. The baffle box is made of 50/1000″ aluminum, although 25/1000″ would be plenty for a box you’re only going to run for a few hours. We plan on getting a lot of work out of this, so we built it heavy duty. You’ll notice that the 12-plate oil cooler is outside the baffle box. Engines run on the test stand traditionally have very cool oil temperatures. I kept the cooler outside the baffle to give the oil a chance to warm up. When set up for flight inside a cowl, the engine will have normal oil temperature and it will be appropriate to have full air flow over the cooler.

Here is the same engine pictured running on this page. We built this engine specifically for the Corvair Personal Cruiser, a single seat aircraft designed for Corvair power. This engine will be installed on the prototype, now under construction. In the photo above, the engine is sitting on the mount for the Cruiser. Shown in silver is the intake manifold for the aircraft. We built this from mild steel tubing. The horizontal inlet is built specifically to mate with an Ellison EFS-3A. Also of interest, note the layout of the sparkplug wires. When oriented like this, the cap can be removed for inspection without removing the wires. Additionally, the distributor can be rotated to set the timing without the wires becoming slack or taut. Doing dozens of engine installations over the years has allowed me to perfect small details that allow the operation and maintenance on the motor to be done far more easily.

Very shortly, we’ll provide the next batch of photos sharing the test data and the calculations. Additionally, we’ll show you the calibration procedure, which allows everyone to understand how accurate this simple machine can be.

Thank you.

William Wynne

Dynamometer testing the Corvair and O-200


Here is an older story of testing from 2004.  It is a good example of how our testing has been an integral part of the work we have done. Although the machinery is simple, the comparitive testing is sound and the meathod is valid. The information gathered in these tests has served builders for a nearly a decade. In the story I mention that the three of us totaled 55 years of work as A&P’s. Today that number is now 84 years of working experience.

O-200 Torque and Horsepower Testing

October 2004


Here’s the O-200 on our dynamomemter, and your test crew from left to right, above: Gus Warren, Detroit Institute of Aeronautics, A&P 1990; Steve Upson, Northrop University, A&P 1976; yours truly, William Wynne, Embry-Riddle Aeronautical University, A&P 1991. While the way we dress may be slow to catch on in high fashion circles, we certainly know our stuff about all types of aircraft powerplants. This is 55 years of A&P experience working on engines in the field nearly every day. This experience, along with a good technical background, puts us in a good position to do real world testing.

On the left above is the Continental O-200 as removed from a 1959 Cessna 150. This engine is considered the standard against which all other 100hp class engines are measured. It is a direct drive 4-stroke, 4-cylinder engine of 200cid. It carries a horsepower rating of 100 at 2,750rpm. I have read that Continental produced about 50,000 O-200s. On the right is a 170cid Corvair engine. For size comparison, the O-200 is 32″ wide without the baffling. The Corvair is 28″ wide.

To adapt the O-200 to our dynamometer required making a new mount. Everything seen in gray, above, is part of that mount. The red cap at the center is a dust cap covering the bearing on which the mount pivots. This red cap is in exact alignment with the O-200’s crankshaft. This way, the rotation against the torque is in line with the crankshaft. The mount was made from a Corvair wheel, a pirated VariEze motor mount, some spare tubing, and a Corvair blower bearing. This bearing is at the bottom, and rides on a steel U channel. This provides additional support to the mount, and restrains it from turning full circle. The vertical element is a 1.5″ diameter steel tube. There is a pin on the back of this tube that engages the hydraulic cylinder. By comparing this mount to the blue Corvair bed mount seen in previous dyno tests, It is apparent how we can change the configuration in a few minutes. This is the charm of using the 5×4.75 bolt pattern wheel as the basic element.

The first photo on this page shows the engine with its stock McCauley prop. Above we see the engine fitted with our primary test prop, a 2-blade 60″ Warp Drive. Since we normally use this prop on Corvairs, the blades here are turned around to work as standard rotation pusher blades. This will effectively load the engine for torque testing. The prop is ground adjustable, so we can fully load the engine at any rpm we desire. The carburetor is an overhauled MA3-SPA. The engine has new Slick mags. It is less than 500 SMOH. We first tested the timing at 24 degrees as per the AD, and then tested it at the pre-AD setting of 28. Differential compression showed all over 70. The engine turned its full rated static rpm with the certified McCauley prop, indicating it was a very healthy engine.

Above is an overview of the test rig. We used two different methods to measure the torque output. First, we used a hydraulic cylinder. This cylinder is located just above and in front of the battery. Second, we measured it with a digital scale. The scale is located just out of view, but it is driven by the 8-foot metal beam clamped onto the mount. We had 4 feet of it extending on each side, so that its weight would not affect the scale reading.

Above is a closeup of the hydraulic cylinder. The braided line runs to a remote gauge. You’ll notice it’s on the opposite side of the stand now. The O-200 has a different rotation than the Corvair, requiring the hydraulic unit to be moved to the other side of the stand. The gauge reading was calibrated by hanging weights on a 4-foot lever arm in 5 pound increments. The needle valve on the output of the cylinder is required because pulses on the line when cranking the starter motor are so fierce, they will damage the gauge. This is true with both the Corvair and the O-200.

In the photo above, you can see the electronic scale sitting off to the side. Pressure is put on the scale by the vertical stick clamped to the steel arm. We’re going to refine this and make it a lot cleaner looking shortly, but for these tests, it worked flawlessly and provided repeatable accuracy. If you’re wondering how all this stayed together in the prop blast, you’re forgetting that the prop is functioning as a pusher. I was only concerned that some of the equipment would be inhaled. Although we got both methods of torque reading to agree, I feel in the future we’ll probably use the electronic scale more often because it’s subject to fewer variables. The dynamometer is also rigged for simultaneous thrust measurement, so we’re going to put the hydraulic unit to that function for simultaneous readings.


After a full day of testing, which included several dozen test runs, we came up with some surprising data. The engine performed substantially below its 100hp rating. I initially suspected that the engine was not performing at peak power, or that the test equipment was flawed. During the testing, we conducted all of the standard mechanics’ tests to evaluate the condition of an engine, including differential compression, timing, and fuel flow. All of these showed the engine to be in good condition. The most telling test was that the engine turned its full static rpm with the certified propeller. It would not do this if it were down on power. Keep in mind that we use a digital optical tach to ensure that there is no error in rpm measurement.

We retested and calibrated the hydraulic cylinder system. It showed itself to be accurate. To doublecheck it, we came up with the digital scale system to corroborate the data. They both told the same story. As an A&P mechanic and a big fan of certified engines, I was very reluctant to conclude that the O-200’s 100hp rating is probably a “gross” rating, as opposed to a “net” rating. If you’re a fan of car engines, you probably know that in the 1960s, many car engines had gross hp ratings. These optimistic numbers had things like the fricitional drag of the engine and the accessories factored out. In the 1970s, net hp ratings became more popular. This is the power output you’d actually see at the prop flange. All of the numbers that we test are net. This is the only type of external measurement we can do. It is also the real world power output of the engine that you are going to use to go flying.

The torque peak of the O-200 occured at 2450rpm. The engine produced 160 foot pounds of torque. If you use the formula Torque x RPM / 5252 = HP, you’ll see the engine was producing 74.6hp. We established the torque peak by running the prop at many different pitch settings until we homed in on the peak of 160.

The hp peak of the engine was very close to its rated peak of 2750rpm. We tested numbers slightly higher than this. However, I was reluctant to run the motor in the 3000s because it’s above the engine’s redline, it’s a borrowed engine, and it’s a certified piece of equipment which will very likely go back into another certified plane. So it behooves us to operate it accordingly. At this rpm, we measured the torque at 144 foot pounds. Using the formula, you’ll see that the engine produced 75.9hp. Again, these are net horsepower numbers.

The temperature outside was 85F, and the RH was 60%. The pressure was almost standard, and we’re only a few feet above sea level. A rudimentary calculation to account for the temperature difference above a standard 59F shows that the corrected hp output of the engine is in the neighborhood of 80-81hp. Again, keep in mind we worked all day in an attempt to raise this output. If you’re reading this and thinking there’s something we’ve missed, I can understand that. It’s difficult to convey the work of three mechanics over a 12-hour period in a few paragraphs and photos, but I can assure you we left no stone unturned in our search. At the end of the day, I largely came to the conclusion that the 100 horsepower rating was a gross rating.

Keep in mind that I’ve been doing installations on planes for 10 years. In this time, we had numerous comparative studies which showed that the Corvair was a very powerful engine, and in many circumstances, could easily match the O-200. One which stands out in my mind was the break-in run of Mark Langford’s Corvair engine at Corvair College #3. He had a pusher prop from an O-200 mounted on his Corvair. The manufacturer of the prop told him on the phone that the Corvair could never turn up the prop to any substantial rpm. When it did, the propmaker was something between impressed and stunned. Even though Mark’s engine is a 3100, it was exceeding what the O-200 could do by a good margin. Over the years, a lot of circumstantial data like this makes more sense in light of finding that an O-200 has a far lower net output than previously suspected.

Does this mean that an O-200 is a bad engine? Does this mean that the VSI in every Cessna 150 isn’t telling the truth? Of course not. The engine is and remains the standard measuring stick of 100hp engines. They have worked for nearly half a century, and will continue to do so. This said, I can assure you from our dynamometer testing that standard displacement Corvair engines will exceed the O-200’s power output handily. This being true takes nothing away from the O-200’s status. It just puts numbers on the success we’ve seen with the Corvair motor over the years.

As a coincidence, a few days after the testing we had a visit from Al Jonic. I worked with Al on the installation of the V-8 in Jim Rahm’s Lancair IVP. Al won the EAA’s highest honor for engineering, the August Raspet Award, for this work. He’s a veteran of thousands of dynamometer runs. Although he’s used much more sophisticated equipment, he was duly impressed with our setup and approach. He offered to send us sophisticated programs to use to correct the conditions for standard day performance. He also offered 40 years of insight on the value of dynamometer runs, correction factors, and gross vs. net ratings.

This dynamometer testing is an ongoing business. I didn’t build it to run it a few times, and prove a few points. I regard it much more as an everyday tool. It takes all the talk out of engine building, and replaces it with hard testing. It is the perfect complement to our ability to rapidly flight test any modification. We’re currently running an entire series of Corvair engine tests. Most of these will be done by Corvair College #8. The Corvair is already exceeding the power output of the O-200. We’re just working to define by how much. When we have this data complete, we’ll put it all on the Web page here.

Thank you.

William Wynne

Fuel Injection – Corvair flight engines reference page


Here is one spot where we have collected a number of different stories on Fuel injection for Corvair aircraft onto a single reference page. Like the other reference pages, it is a central starting point on the topic, and easy to keep updated or make additions to. If you are interested in learning more about this topic, read on, there is a significant amount of information here.

If I were to pick a single topic that new builders are interested in, but know little about the applications of, It would be Fuel Injection. This is a topic dominated by misconceptions and myths. Here is a quick check: Do you think that an port fuel injection engine or one with a carb on a long intake manifold makes more power? Would you be surprised to learn that the evaporative cooling effect of the carbs fuel delivery can give it a significant advantage? It does, and to learn this and many other points on reliability, read on. Unlike much of the info on the net from armchair experts, the information below is straight from experience and testing…in aviation settings, not in cars.




The information below is in the following order:


1) Links to stories I have written on FlyCorvair,net

2) A full print of my Group numbering system #3700 EFI notes.

3) A reality check story from 2008 on EFI failures

4) Notes on Internet ‘experts’ you should beware of

5) A 385 mph EFI plane and some final thoughts.


Above, a rear view of the Panther engine. Mounted on the intake is a Precision Mechanical fuel injection system. Initially, these was the planned fuel system for the Panther, but after careful evaluation, Dan Weseman opted to go with a very simple MA3-SPA carb. All of the aerobatic flights on video on the Panther site are done with a one barrel aircraft carb, not injection.




1) Links to stories I have written on


Click on the titles in color to read the full stories:


Mechanical Fuel Injection Testing

Compares Precision and Airflow performance instalations

Fuel Injected Corvairs

stories on 3 running EFI engines

Group Sources for the new numbering system.

Covers that EFI is Group  #3700 and Mechanical injection is Group #3800.

Panther Prototype Engine 3,000 cc/120 hp to OSH

Another look at the Precision system

Corvair Powered Davis DA-2, w/EFI

The only successful flying EFI Corvair powered plane. A hard won achievement.




2) A full print of my Group numbering system #3700 EFI notes:


3700- EFI (Electronic Fuel Injection)


Many people just arriving in aviation are interested in electronic fuel injection.  Some homebuilders are impressed with its performance in cars or have read about one of the handful of experimental aircraft flying with fuel injection. After listening closely to builders, I discerned their interest originated from five reasons: 1) They thought it would make the engine more powerful; 2) They thought it would reduce fuel consumption; 3) They felt that it would eliminate the possibility of carb ice and eliminate the need for carb heat; 4) They thought it would be more reliable than a carb, or; 5) They just wanted to try it. Experience has shown me that the first four are not true to any meaningful degree, and that #5 is the only reason that makes sense. If you are pursuing EFI for reasons #1-4, you are going to be disappointed, but if #5 is your motivation, then the project may be a success to you.

Let me first say that I am not against EFI, but I think that builders should know the facts before they pursue it. My background on EFI installations in planes is better than most. A guy who works on them all the time in cars, but doesn’t put them in planes, has a long way to go before he learns what he needs to know to be reliably and safely flying. I did a lot of work on Jim Rahm’s 427 cid V-8 Lancair IVP. It had the best EFI system in the air. We had the best people working on it, a nearly unlimited budget and experience that no homebuilder in his garage could match. It took a lot of very hard work to make it the reliable system. Just because Jim’s motor made 600 HP and you only want 120 HP doesn’t mean that solving the installation issues will only cost you 1/5 the time and money. And even if it did, we would still be speaking of time by the calendar years and money by the cubic foot. When I read discussions on the Net about EFI on experimental aircraft, I can quickly tell who has never assembled and flown a system.  95% of the advice on the Net is offered by people without flight experience. Out of the 30,000 experimental aircraft in the U.S., I am fairly sure that less than 300 of them have EFI. I cannot think of a single significant aviation record below 500 HP that is held by an EFI engine. There have been many clever people who put a lot of effort into EFI on planes, with little result. No matter what caliber of auto mechanic you are, experience says that you will find exceeding the performance of carbs or mechanical injectors very difficult, and EFI may never have the reliability record of the simple 1 barrel carb.

Out of the roughly 300 experimentals flying with EFI, the vast majority of them are using 1990s auto engines with EFI from the factory. In this case, the factory engineers did most of the work. If you think about it, there are very few motors like O-200s, VWs and Corvairs flying on EFI. And the ones flying can’t boast the flight record of carbureted engines. I have seen a number of these planes flying with 35psi fuel pumps inside the cockpit with barbed hose connections and hose clamps. No one should dream of flying things like this. Let’s examine the points one by one objectively to learn about the issues and make an informed decision.

1) I have seen claims that EFI makes the same engine 30% more powerful. Nothing of the sort is true.  Engines make power because they burn a mass of air mixed with the right amount of fuel. There is no way that an engine is going to inhale significantly more air because it doesn’t have a venturi carb. This advantage is slight, and would be well below 5% on an engine like a Corvair. To see any more difference than this, the cylinder heads and intake tract would need to be designed for it right from the start, by very smart people with a lot of sophisticated equipment (of the caliber found in Detroit factories). Slapping an EFI system on the Corvair will not have the same effect. Fuel injected motors are said to make slightly more power because the fuel is better atomized. But carbs, even simple ones, are surprisingly good at this. The amount of records still held in racing by carbs should tell anyone that the EFI power advantage is minimal. Carbs have a very serious advantage of vaporizing the fuel well upstream, and having the air/fuel mixture cooled and its density increased. In almost every case, this offsets any gain in power from atomized fuel. When running at power, Corvair intake manifolds are cold to the touch from vaporizing fuel. EFI does not have this effect.

2) EFI will not significantly reduce fuel burn in a Corvair engine. For best economy, engines need to run a lean mixture. EFI has the theoretical ability to atomize fuel slightly better allowing it to run slightly leaner mixtures than a carb could without detonating. In actual use, it is foolish to run an engine this close to detonation. Modern auto engines can do this because they have computer-controlled ignition tied to a knock sensor and the fuel injection. Without these devices, any significant fuel burn advantage is lost. Many of the well known auto power proponents, even those who work with computer controlled EFI engines, clearly state that EFI doesn’t significantly reduce fuel burn for a given HP in aircraft engines. The efficiency advantage in cars is gained by running in “closed loop” with air/fuel ratios near 14:1. Under this operation, the injectors are fine tuned by reading the O2 sensors many times a second. The reality that few new builders understand is that any engine running at 75% or more power has to be running an air fuel ratio of 12:1. At this setting, O2 sensors don’t reliably work, and the system will operate in open loop, forfeiting any efficiency gains while retaining all the complexity and vulnerability. I have never seen any EFI flight engine that will fly at cruise power in closed loop mode. They are all just operating off a set of pre-programmed values based on RPM and MAP. These can be very crude, as some aftermarket EFI systems have RPM increments as rough as 250 RPM. In cars this would be masked by the O2 sensor moderating the injectors, but it can’t when it is in open loop. It is technical reasons like this that allow carbs to often demonstrate smoother operation than EFI in experimental aircraft.

3) EFI is less prone to carb ice, but is not immune to this trouble. There are still conditions that can cause this trouble. Almost all injected engines have an alternate air source. Homebuilt aircraft in Canada are required to have heated alternate air no matter what the fuel system is, and there is good logic to this. For a more complete discussion of this, see the article on carb ice at the end of the Manual.

4) Many people feel that EFI will free them from things like carb ice, reducing their level of risk in flight. While the risk of carb ice would be reduced for a pilot too careless to use carb heat, many new risks are introduced. EFI requires high pressure pumps, regulators and lines; it can be stopped by a piece of trash in the fuel that a carb would easily pass; its numerous electrical connections are prone to failure by corrosion or poor crimping; and the whole thing is so electrically dependant that most people fly with two batteries. Contrast this with a gravity feed fuel system in a plane with distributor ignition which will run for hours on a small battery with no input from an alternator. You cannot focus on the one possible advantage of a system without considering all the downsides that come with it. Automotive EFI installations are reliable today because auto makers spent literally billions to make them so. Brilliant people in Detroit who are specialists in dozens of details of the installations and privy to incredibly accurate statistical data on failures allow them a great corporate body of experience to tap into with every installation. It is my feeling that anyone looking into EFI who states that it is more reliable is making an argument for the car, not what an individual homebuilder can do in a plane, where a single detail of installation may compromise the system.

My observations on reliability are simple: Any system that uses lower pressure fuel is less likely to leak. Gravity is better than 5 PSI, and 5 PSI is better than 40 ; any system that uses no electricity is better than one that uses  a little, and one that uses a little is better than one that uses a  lot, especially if the one that uses a lot needs it to be a  certain voltage; any system that has less parts and connections is less likely to  fail,; digital electronic connections, working a low voltages, are very sensitive  to corrosion, temperature, and vibration, things planes produce more than newer  cars.

5) Being an experimenter at heart and wanting to address the challenges of an EFI installation is a valid reason for trying it. You know a good, reliable and airworthy system is quite a challenge because you don’t see them often. Anyone who achieved this could be justifiably proud of his creation and would learn a lot along the way. A person who is motivated by this will be satisfied when it works, whereas people motivated by #1 – #4 are bound to be disappointed when EFI cannot live up to the overblown claims many armchair/Internet experts make for it. The only good reason to work on an EFI Corvair is because you want a challenge, and this is more important than finishing your plane soon, or operating at a lower risk level. This is a valid position, and I support anyone who knowingly makes it.




3) A reality check story from 2008 on EFI failures:


” A Christmas story”

 At 8 a.m. on December 24th 2008, I was driving my 175,000 mile EFI S-10 up I-95 at 75mph. I had promised my parents that I would make it to their house for Christmas Eve dinner. I had never had a bit of trouble with this EFI engine. Near Richmond, Va., it quickly died out, and I was only able to coax it into a truck stop at 10% power. A morning of diagnosis showed that the pressure regulator had died. It was not in an easy place to get to, no one had a replacement and the truck was worth maybe $500 before it was broken. I gave the truck to a 20-year-old tow truck driver wearing a Chevy hat and a Jack Daniels sweatshirt, as a trade for a ride to a car rental place. We got there 10 minutes before they closed. The driver asked me several times if I was really giving him the truck and if I really was from New Jersey. The experience was counter to many things he had been told about people from N.J.  After some reservation, he took the gift of a truck from a Yankee on the eve of the birth of Jesus to have special significance.

 Such a warning less failure in a plane might prove to be lethal. Note that aircraft carbs almost always run even when they are having an issue.  A good look inside Pat Panzera’s Contact! magazine issue #96 shows a destroyed homebuilt aircraft, product of a sudden EFI failure. Here is a story of a guy who may have felt that carbs and engines without O2 sensors were stone age. Maybe, but stone age tools are noted for reliability. I am glad the builder was not more seriously hurt. Over the years, a number of people have written to explain that they are going to engineer their own EFI systems, or use something called “shareware” to program one (the blind leading the blind on the Net). Out of perhaps 50 people who have written this, not a single one of them went on to produce a running EFI engine. Experience tells me that people who arrive with a big flourish and little consideration for what has been accomplished have a very low chance of flying anything.




4) Notes on Internet ‘experts’ you should beware of:


A modest search on the internet will reveal many people speaking about EFI for Corvair powered planes. Armed with the information I have printed above, you can debunk most of the claims people make. Still, there are people who present a case to new builders as if they are some type of experienced expert to be followed.

The internet is an odd storage device. I holds more old trash better than any landfill on earth, and it keeps it fresh, even long after the project was abandoned. Let me share by example: Don’t waste the time to look it up, but there is a long detailed website run by “Haynes Engineering.” Sounds official, but it was just one guy in a barn who had never built a flying plane before, offering a long how to session on putting EFI on a Corvair in a Zenith 601. I never met the guy, but I did email him several times, and he spent a long time on Mark Langford’s discussion list, where he had many fans who eagerly awaited Mr Haynes demonstrating all the things he promised from is Harley Davidson salvaged system. Although I offered to publicly test run his engine at a college, Mr. Haynes soon despised me, probably for not recognizing his brilliance. His website is all about putting a Corvair on a 601, but makes no mention of Our success with doing this, or my work at all.

If you have built planes, it was easy to see that Haynes didn’t know much about planes, but had the kind of ego that didn’t like admitting that. He was a foolish cheap skate, ‘rebuilding’ his engine with a used cam and worn gear, and using angle iron to build a motor mount. His EFI system had hard aluminum lines where it needed flex ones, and he spent a lot of time trying to use a little outboard starter. In the end, after getting many green guys excited, he couldn’t make the engine run, and instead started it for 5 seconds on starter fluid, and then wrote a post to the internet silmaltainiously declaring victory and quitting airplane building altogether. Does this sound like a stable person who you can learn from? Is it the kind of information that you want to bet your life on? This was years ago, yet I saw the website just last week, with no mention of the system never working or the whole aircraft project being abandoned.

If you are new to home building, the quicker you learn never to be distracted for real progress by day dreamers and fools without experience, is the quicker that you will learn what really works, and how to incorporate these skills into your own experience and your own plane. The internet will provide an endless stream of people like that. 80% of the people who start a homebuilt do not finish. Be determined to be in the 20%. One of the things that the 20%ers all have in common is not getting sidetracked by fools.




5) A 385 mph EFI plane and some final thoughts:


I’m known for advocating simplicity in aircraft engines. This recommendation comes  from my experience on the opposite end of aircraft powerplants. Above,  Arnold Holmes (host of CC#17,#25, #29) and I stand behind the engine installation on a V-8 powered Lancair IV-P.  This is an EngineAir package that I helped develop from 1993 to ’98. It’s 450hp, geared,  injected, intercooled and turboed, and features air conditioning. Get a good look at the size of the 5-blade MT propeller.

  Eventually, about a dozen of these took to the air. They were stunning performers. I flew  from Oshkosh to Daytona Beach in three hours and five minutes in our first airplane, N420HP. This aircraft is on the cover of Sport Aviation in July ’97. If someone suggests I don’t understand EFI, ask them if they have flown in a 385 mph EFI plane they helped develop and build.

 The development of this engine took the work of many clever, dedicated people, and one  guy with cubic yards of money, Jim Rahm. It worked, but taught me that homebuilders at all levels  tremendously underestimate the effects of complication, primarily its delays and expenses.  Whenever I read discussions about electronic injection or computer controlled engines, I  can tell in an instant who has no practical experience with attempting to prepare these  systems for flight.

Evaluate your interest in fuel injection carefully. for most builders, it is a distraction, for some it will become a stumbling block, for a tiny number of people it may become a dangerously complex part of their plane, a part they thought would be the most reliable, but turned out to be the part they trust the least. This is pretty far from the goals that most people have when the first think about putting EFI in their plane.-ww

Getting Started Reference page


Below are links you can click on in sequence that follow through a detailed series I wrote on Getting Started in Corvair building. They are detailed and long, but successful builders tend to spend the time to learn and make better choices. I wonder about people who decide to buy an engine or a plane of any kind after reading a 4 page sales brochure with less than 200 words on it. Hardly due diligence in a ‘flyer beware’ marketplace. If you would like to start with a simple three page spec sheet on the engine, read this link first: Basic Corvair information

Conversely, we offer a very detailed picture of exactly what Corvairs are about, what you can learn and achieve by building one, and the infinite ways you can build one that will conform to you needs, goals, skills, timeline and budget. The Corvair can be made to fit your project, you don’t have to rearrange your plans and budget to serve the company that is selling you an engine. Sounds funny when you put it that way, but that is just what most people do.

I could drive myself to madness by concerning myself with what the masses will or might do. In experimental aviation you don’t have to be concerned with what ‘most’ people are buying or doing (unless your goal is to be like everyone else rather that being yourself), you need only find the right path for you. Corvairs are not for everyone. The strongest appeal are to homebuilders with traditional goals of Learning, building and flying. Many people interested in experimental aviation today have short attention spans and shallow goals. They want to posses skills but are unwilling to learn; They want to have things but are unwilling to make them; they are unable to differentiate between going for a ride in a plane and being an Aviator.

If you want to learn, I have long proven I have things to teach; if you wish to build and be the master of your engine, we have a proven path; If you long to find your place among real aviators, we have a home for you. You do not need any prior experience, just a willingness to learn and a positive attitude. In 24 years we have shared our experience with hundreds of builders. If your goals match our strengths, we will be glad to work with you. -ww.

Getting Started in 2013, part #1, Crankshaft process options.

Getting Started in 2013, Part #2, Group numbering system

Getting Started in 2013, Part #3, The Camshaft Group (1100)

Getting Started in 2013, Part #4, Case Group (1200)

Getting Started in 2013, Part #5, ‘Allan Able’ short block.

Getting Started in 2013, Part #6, ‘Bob Baker’ short block

Getting Started in 2013, Part #7, ‘Chas. Charlie’ Short Block

Getting Started in 2013, Part #8, ‘Davie Dog’ Short Block

Getting Started in 2013, Part #9, ‘Eddie Easy’ short block.

Getting Started in 2013, Part #10, Piston and Cylinder options.

Getting started in 2013, Part #11, Comment of the day

Getting Started in 2013, Part #12, Piston Choices

Getting Started in 2013, Part #13, Basic piston/rod/cylinder combo.

Getting Started in 2013, Part #14, 2,850 cc piston/rod/cyl. Kits

Getting Started in 2013, Part #15, 2,775cc, (imaginary piston)

Getting Started in 2013, Part #16, 3,000 cc Piston/cylinder kits

Getting Started in 2013, Part #17, Short block cost chart.

Getting Started in 2013, Part #18, A look ahead

Getting Started in 2013, Part #19, Cylinder Heads

New Numbering System, Final, please print.

Zenith 601/650 – Corvair reference page November 2013


Here is a single location page that has a great number of links to information specific to the Zenith 601/650 / William Wynne-Corvair Combination.  It is a particularly good match, we have a number of different ways to approach it that serve the needs of many different builders, and it is a success story that builds on our 10 year history of working with Zenith builders, starting with our own personal 601XL in 2003. Since then we have assisted more than 80 builders to complete and fly their Corvair powered Zeniths.

If you already are working on your Corvair, this page will have information you have seen already on our websites, but I have included it so that this page can function as a ‘stand alone’ guide for 601/650 builders who have just heard about our work with the Corvair. Our approach to serving builders is different than typical businesses geared only to sell things to consumers. Our goal is to assist you on your path to becoming a more skilled aviator. The products we sell support this, but simply getting you to buy things is not what I am in aviation to accomplish. If you would like to start with a simple three page spec sheet on the engine, read this link first: Basic Corvair information

This page is broken into the following sections:


1) Introduction

2) Engine and build options

3) installation components

4) Support for builders

5) Flying 601/650s

6) Builders in process

7) 601/650 flight data and safety notes

8) who is WW?

9) Comments on dangerous trash.


At the end of each section there are links to supporting stories that have expanded information on concepts discussed in the section. Take your time and study it carefully.

I will be glad to answer further questions just email or call 904-529-0006. You can also check our two websites, , . The first is our ‘newspaper’ the second is our ‘library’ and ‘store.’ The links below are stories that already appear on these two sites, they are just arranged here to support this introduction to Corvair power for 601/650 builders.

Above, Phil’s Maxson’s 601XL airborne over the Florida coast at Ponce Inlet, 2006. Phil finished the plane in our Edgewater hangar and has been flying the plane ever since. It has proven to be economical and reliable over the long run. Phil is a skilled manager from the Fortune 500 world of business and could have purchased any engine on the market, yet he selected the Corvair as the best match to his personal goals of Learn Build and Fly.-ww


1) Introduction:

The Corvair has been flying since 1960, and I have been working with them as flight engines since 1989. It is a story of careful development and testing, a slow evolution to the engines we have today. It is ‘old and proven’ rather than ‘new and exciting.’  If that approach appeals to you, read on. There is a lot of material here, and it isn’t something you are going to absorb in one quick scan. Frankly, your engine selection deserves careful consideration, and it isn’t the kind of decision you should make based on a 4 page sales brochure.

Corvairs have proven themselves to serve a very broad variety of builders. Many alternative engine options for the Zenith are offered only as a “buy it in a box” import, more of an appliance than a machine, with little or no consideration of the builders, skills goals, needs, budget or time line. The Corvair has options to address these valid considerations, because your power plant should conform to you, not the other way around.

This said, Corvairs are not for everyone.  In the 25 years I have been in the EAA and working with builders, the Corvair has always been very popular with ‘traditional homebuilders’, the people who have come to experimental aviation to discover how much they can learn, understand and master.  The expansion of the EAA has brought more of these builders, but it has also brought a great number of people incapable of distinguishing between mastery of an aircraft or an engine and just merely being its buyer and owner.  People who’s consumer mentality and short attention spans are better suited to toy ownership than mastery of skills and tools in aviation. Corvairs, and perhaps experimental aviation, are a poor match for such people. Many salesmen in our field will gladly sell anything to anyone with green money. I am an aviator, not a salesman, and the gravity of the subject requires more frank discussion and ethics than many salesmen bring to the table.

If you came to experimental aviation to find out how much you can master, not how little, then you are among the aviators who follow Lindbergh’s timeless 1927 quote: “Science, freedom, beauty, adventure: what more could you ask of life? Aviation combined all the elements I loved.”  Even if you are brand new to aviation, I am glad to work with you. I have a long history of working with builders of all skill levels. We have a number of successful builders out flying their Zeniths who are the masters of both their airframes and engines, who had never changed the oil in a car before building their plane.  If you got into experimental aviation just to buy stuff, then any salesman will do just fine for you. If you got into experimental aviation to learn, develop your own skills and craftsmanship and make things with your own hands, then who you work with really matters. You can’t become and old school homebuilder / motor head by buying things from salesmen. They have nothing to teach you. What you will do in experimental aviation is not limited by what you already know. It is only limited by what you are willing to learn, and selecting experienced people to learn from.  If you are here to learn, I am here to teach. It is that simple.



a) – Complete Lindbergh quote is here: The Quote, 1927, C.A.L.

b) – Explanation of machines vs appliances : Machines vs Appliances Part #2

c) – Story of real engines vs ‘ideal’ ones: Unicorns vs Ponies.

d) – An example of our ling standing working relationship with Zenith: Friday out of shop until 4pm.

e) – A direct explanation of what makes my work different than typical LLC’s : 2011 Outlook & Philosophy

f) – A moving statement of philosophy: Sterling Hayden – Philosophy


Above, the 3,000 cc Corvair, configured for a Zenith 601/650. An inherently simple engine, It’s opposed six configuration makes it the smoothest of available power plants. It has outstanding cooling because GM put a tremendous amount of cooling fins on it and  gave it a factory CHT redline of 575F. All of our engine parts are made in the United States.


2) Engine and build options:


If you are new to Corvairs, lets quickly cover some ground: General  Motors made 1.8 million Corvairs. brand new parts, including billet cranks, forged pistons, valves bearings,  virtually every single part inside is currently made and readily available, and will remain so. Rebuildable Corvair engines are plentiful, and much easier to find that Lycomings or Continentals. We have been working with Corvairs for 25 years, and there is no shortage of core engines or parts. If you doubt this for a second, Google “Corvair engine parts.”

The Corvair makes an outstanding aircraft engine because it is a simple, compact, direct drive, horizontally opposed six cylinder, air cooled engine. It is robust, and ‘flat rated ‘ from it’s automotive output. The engine runs equally well on automotive fuel and 100LL, and it does not care about ethanol. In its 53 year flight history, more than 500 experimental aircraft have flown on Corvair power.

The engine can be built in three dispacements with three respective power outputs. They are 2,700cc / 100HP, 2,850cc / 110HP and 3,000cc / 120HP. The two smaller displacements weigh 230 pounds, the larger actually weighs 8 pounds less because it uses lighter cylinders. All engines are completely rebuilt from very high quality parts before flight. They are not just removed from cars. The parts we use are specifically selected to convert the engine for the rigors of flight use. Forged pistons, Inconel valves, chrome rings, ARP rod bolts and many other components are upgraded in the rebuild.

To absorb the propeller and flight loads a “5th bearing” is added. It is a billet housing with a very large bearing from a V-8, bolted on the end of the case.The ignition is redundant and utilizes two 40,000 volt systems, one driven by digital electronics the size of a match book, the other by a traditional set of points. The engine is direct drive, it has no complex reduction unit. It makes good thrust because it has more than twice the cubic inches of a Rotax 912. All of the systems on the engine are intentionally patterned after those on Lycomings and Continentals, because they are the  model of success in proven aircraft power plants. People who do not acknowledge certified engines as excellent models of success are often just zealots.  To succeed in experimental aviation you need dispassionate information not emotional opinion.

One of the unique features of the Corvair is that it can be built at home, from our information and parts and a locally acquired rebuildable engine, or it can be purchased from us, test run with logs. 90% of current builders are building their own engine at home. Only 10% of the builders opt to have us build their engine. We have happy to serve both builders. In either case, Corvairs are the best match for builders who want to understand and be the master of their engine.

Because of the plans built vs production engine nature of the Corvair, there are large variations in how much builders budgets run. Below is a quick look at the differences. Keep in mind, these budgets are for first class, completely overhauled, zero timed engines with 5th bearings, starting, ignition and charging systems. We have clever builders who have built and flown engines for less than $3,000, but this not representative of main line builders. The numbers below are much better for Zenith builders to budget on.


2,700cc / 100HP typical homebuilders budget: $6,500- Same engine assembled and run from us $9,750

2,850cc / 110HP typical homebuilders budget: $7,500- Same engine assembled and run from us $10,750

3,000cc / 120HP typical homebuilders budget: $8,500- Same engine assembled and run from us $11,750


If you are attracted to the concept of building your own engine, but have not built motors before, Good.  About half of our builders have never built any kind of an engine before. Our main work is teaching people what we know and providing the parts to work with. Our system does not require anyone to be a machinist nor to have previous engine experience.

The procedure of building an engine in your shop follows this format:

1) Get a conversion manual and DVD’s from us, use them to find a rebuild able core engine locally. Disassemble this engine following the steps in the DVD.

2) Send the crank and heads to our approved facilities for rebuilding and modification. They come back ready to ‘bolt on.’ Other parts of the engine are cleaned and inspected. The parts to convert the engine are ordered from us, many of the standard rebuild parts like lifters and gaskets are available from local auto parts stores. We do not ‘middle man’ anything you can directly buy.

3) Assemble these parts according to the manual and DVDs. There is no machine work required, only basic tools are needed, and a few specialty tools like a torque wrench. Many builders attend our free Corvair Colleges and directly learn hands on skills. You can even bring your parts and assemble them under our supervision, and test run your engine on our equipment. College attendance is a plus, but not required. Our methods work without direct training; a good number of engines are built and flown each year by builders who have never met me in person.

4) The test run serves several purposes. We teach people to build one of  three specific models, and we teach them to use specific parts. Not only are these proven, but it also allows me to verify from a remote location that the engine was assembled correctly. A builder can report his static rpm, CHT, oil temp during the test run with his Warp Drive prop at the specified setting, and I can confirm the output and assembly of the engine without seeing it personally.

If you would like a sample of the information on working your way through the above four steps, get a look at this: Getting Started in 2013, part #1, Crankshaft process options.

I have broken down building a Corvair and installing it on your airframe into 42 “groups”. The previous link is about  ‘Group 1000′ the crankshaft. If you would like to look at every part that goes into a Corvair, along with the conversion parts we sell, look at Groups 1000 -3300 at this link to our catalog:

All builders get started with a conversion manual. The first part of the above link is about manuals and DVD’s.  The direct link to the manual is: almost all builders looking for a rebuild able engine also order the Disassembly  DVD, which covers core engine selection visually. The direct link to it is: We encourage everyone to get started with information, even if you are pretty sure you would like to purchase a production engine from us. If you eventually buy an engine from us, we directly reduce the price to rebate all the money you spent on manuals and DVD’s.



a) – Corvair Weight story: Corvair vs O-200…. weight comparison

b) –  Samples of our production engines:  2012 Corvair Engines For Sale: 100, 110 and 120 HP

c) – For an explanation of ‘flat rating’ and a Zenith engine build : Shop perspective: Mastery or ?

d) – A story about engines running on our hangar Dyno:

e) Engine of builder now working on Zenith airframe: World’s Strongest 3,000cc Corvair, built by Greg Crouchley

f)  2.700cc engine we built for Becky Shipman’s 650: Shipman Engine at CC#22

g) A story about the evolution on 120HP Corvairs: 3,000 vs 3,100 cc Corvair engines.


Above, a 2009 photo from our workshop. I kneel in the workshop next to motor mount Number 100. This sounds like a lot, but I made the first one in 2003 for our own 601 XL.  Most experimental aircraft companies, both large and small, fail because for two simple reasons; First, the ownership cannot physically make the product the sell, and second, their financial backers are unwilling to go several years before seeing the payoff.  We succeeded because I am a craftsman first, and can make all the parts in the catalog, and we have never had, and would not accept having any partners nor investors. The Blue fixture is the one we use for the 601/650.


3) Installation Components for the 601/650:


We provide every single part it takes to install a Corvair in your 601/650.  You can buy them one at a time, or all at once. Our Zenith 601/650 installation, which has been successfully flying for a decade, is a long proven system that has only seen a few very minor detail evolutions. Our Zenith installation manual detail how and why each of the installation components are installed on your airframe.

The installation does not require any modification to the airframe fuel system like most EFI engines do.  Being air cooled and carbureted, it is one of the easiest engines to install. Many companies that are good at selling things are poor at teaching things, like how to install their products. Teaching is the very cornerstone of my work, I am a skilled writer, we run Corvair Colleges, and we have a simple engine. All this adds up to a comparitively easy engine to install. There is no need to rush it, but I can do it working in one long day.

 Installation part numbers are Groups 3400 through 4300 in the second half of our numbering system. Get a look at this link: From that list, you can see that the major installation parts for a 601/650 are: #3601(S) intake manifold, #3901(A) Stainless exhaust, #4002 spinner bulkhead, #4003 Warp Drive prop, #4101 baffle kit, #4102 nose bowl, #4103 cowl kit and a #4201(A) mount. The other smaller items listed are detail in our Zenith installation manual. All of the above parts have links to stories through the products page.

Many people new to building initially think that very economical engines like the Corvair must also be inexpensive to install. In reality, the cost of items like motor mounts and cowls are not affected by the cost of the engine they mount and house.  A mount for a $30K UL-350 and a $7K Corvair have about the same amount to tubing and welding time in them, and thus cost about the same. Most engines for Zeniths have installation kits that run from $4,000 to $6,000. The Corvair is near the bottom of this range, but the savings of using the Corvair is in the engine, not the cost of installing it. Builders can save a significant amount of money by fabricating many of the parts like #4103, but most people are near the finish line at that point and opt to buy it and save the time. Exact cost on the installation parts varies a bit, I will be glad to review it with builders after they study the installation manual.


a) – For an example of 74 years of aircraft welding talent: Zenith 601/650 Motor mounts, P/N 4201(A)

b) – To learn about the Stainless exhausts we make: Stainless Steel Exhaust Systems

c) – Louis Kantor’s 601XL running for the first time in our front yard:

d) – The same aircraft on its first take off, from our airport. July 2009.


Above, 2004 at Oshkosh: Next to our personal Zenith N-1777W, I explain our dual ignition arrangement two executives from Falcon insurance, The EAA’s provider. To offer real support, an alternative engine provider must be an effective advocate for his builders on many fronts, including meeting the requirements of underwriters. Just being an engine guru is not nearly enough. Corvair engines that follow our design,  including to ones assembled by builders, are fully insurable at the lowest rates, right from the first flight, because they have an outstanding safety record. Having good effective hands on support is a critical element in this outstanding record.


4) Support for Builders:


Beyond the basic engine and installation components, we offer many forms of support to Zenith builders:


a) We have a very detailed Installation manual for all Zeniths: We also have a flight operations manual with specific test flight plans and procedures:


 b) we hold 4 free hands on technical seminars called “Corvair Colleges” every year. This includes an annual College held in Mexico MO at the Zenith Factory timed to coincide with the factory open house in September. For an introduction to Colleges, read this link:  An overview of upcoming colleges is at this link:  Upcoming events, Airshows and Colleges #26-28. If you would like to see video of a College, here is a link to Corvair College #17


c) The “Zenvair” group is a separate on-line peer-to-peer discussion group just for Corvair/Zenith flyers to directly and freely share information and data with each other in a civilized productive format. The link is : ‘Zenvair’ Information board formed  This is very effectively moderated by Zenith/Corvair builder and flyer Phil Maxson who’s 601 is pictured at the top of this page.


d) Woody Harris, subject of this story:  Zenith 601XL-2,850cc, Woody Harris Is our west coast representative. Although we have held 5 Corvair Colleges in California, including 2 at Zeniths west coast facility Quality sport planes,  we only make one trip to the west per year. Woody covers all the shows and events from Arlington to Copper State when we can’t be there.


e) I am the last guy in aviation who still makes free house calls. Over the years I have made more than 400 in person visits builders projects. I travel extensively, and go out of my way to include builders workshops on these trips.  These stops and the colleges allow me to really understand the needs, strengths and dreams of rank and file builders that no one can read in email or at an airshow. for a sample, read this story: Corvair House Call, Range: 335 miles.


f)  By my continued advocacy and industry relations, Corvairs have full insurance, at the lowest rates, available from a number of sources. If you would like to find out more Contact Bob Mackey, VP of Falcon insurance, The EAA’s designated provider, seen on the left in the photo above.


g) Over the years, we have built a very tight knit community of like minded builders. If you read this story about fools at our county airport: A visit to the insane asylum, and it sounds like your airport, and if your local EAA chapter is devoid of homebuilders and filled with negative people, you will find the Corvair movement to be a powerful antidote. Many Corvair builders catch several colleges a year, there they find positive, outgoing, energetic builders, effectively making the Colleges their “local EAA chapter” We have worked very hard to attract outstanding people interested in accomplishing their goals. I  go out of my way to encourage new builders but I am intolerant of people who are compulsively negative. I am willing to be a cheerleader, but not a therapist.



Above is Rich Whittington’s fabulous looking 601 HDS at Corvair College #21. Our Conversion Parts work with all models of the 601 and  the 650. One of the things I respect about Rich is his outspoken honesty. He started out with a criminally poor 2,700 made by a rip off artist in GA. To prevent other builders from making a similar mistake, he wrote a number of comments on this on Zenith Builders and flyers page. His second engine was a standard installation matched with a 3,000cc engine his is very pleased with.


5) Examples of flying Corvair Powered Zenith 601s and 650s:


In 2011, I wrote up a quick list of flying Zeniths, Since then a number have been added, but this list is a good beginning point, it has date of first flight and the N-number of these aircraft. Click on this link:  List of Corvair Powered Zeniths

If you would like to get a look at pictures and short notes on a number of 601/650’s, click on this story link:

16 Flying Corvair powered Zenith 601/ 650s

Below are a number of stories about flying planes.  We get a steady flow of new flyers Like Jerry Baak and Pat Hoyt, whos names are not on the first list:

 A really nice 2700cc tail wheel XL:  New Zenith 601 XL(B), Conventional Gear, Jerry Baak, S.C.

Good looking 2,700cc plane in FL, story is about a house call: Flying 2700 cc Zenith 601 XL(B), Alan Uhr

Very nice looking 650, links to movies of plane: Zenith 650-2700cc Dave Gardea

Our west Coast rep, Woody’s plane: Zenith 601XL-2,850cc, Woody Harris also read the story: Woody’s 2,850cc Corvair/601XL hits 400 hours.

A plane seen at Brodhead, Oshkosh and the Zenith open house in 2013: Patrick Hoyt, new Zenith 601XL, now flying, N-63PZ

Story from the moderator of our “Zenvair” discussion group: Guest writer: Phil Maxson, flying a 3100cc Corvair in his 601XL

Story on a long time member of the Corvair Community: 601XL-2700cc Dr. Gary Ray

Story on a 500 hour 601 Tail Wheel aircraft: Zenith 601XL-3100cc Dr. Andy Elliott


Above, Making a house call in California to Larry Winger’s. His engine ran at Corvair College #18. Larry’s aircraft is a magnificent 650, built from plans, not a kit. The aircraft has since been completed and has been moved to the Chino airport. Larry exemplifies many of the finest qualities in homebuilding. When he started the project, he had never built an engine, a plane and was not yet a pilot. He has since accomplished all three.


6) Examples of Builders working on this Combination:


Many experimental aircraft companies like to tout how many of their product has sold as a measure of  success. Sales numbers on only a measure of their success, not that of builders. The only number that counts are how many builders that make it all the way to flying and enjoying their creation. It is a fact of marketing that it is far easier to keep finding new buyers to spend money than it is to support the ones that already spent the money, all the way through flight.  This is why many aircraft LLC’s have planned lifespans of only 48 months, so they make all the sales and fold up the tent before they have to do the real work of supporting builders.

We are very different. I have been supporting Zenith builders for a decade, but I have been working with Corvair builders since 1989. I am in this for the long haul, and my measure of success is getting people flying. We have many people working on Corvair powered 601s and 650s. In the first 10 years, we build and sold about 160 motor mounts for the combination. I didn’t make them just to have something to sell, I made them so that each builder would have a good shot at completing and flying his plane. I will be here long enough to support each of those builders in completing their plane. If you select a Corvair engine, I will be your ally in completing your plane, just as I have been for many others before you.

If your goal is to merely buy something, you need only find a salesman with an engine to sell. If your goal is to learn about, understand, build and fly your plane, you need an instructor-guide-mentor, an aviator not a salesman. Think it over: If your goal was to climb mount Everest, there would be plenty of people you could buy equipment from, but that isn’t the same thing as finding a Sherpa who has been to the top to act as your instructor and guide.  A big part of why experimental aircraft have a 20% completion rate is that most people purchasing a kit or an engine have not spent 3 minutes learning how to differentiate between a salesman and a guide.

Below are a sample of our builders, each of whom I am going to see all the way through their aircraft finished and flying:


Nice guy who has been to many Corvair Colleges: Jim Waters 601XL-B project, “In The Arena,” Memorial Day 2013.

Our oldest builder in action :Dick Otto in California, S.R.B. (Senior Ranking Builder)

A letter from the same builder: Mail Sack – Letter of the month – Dick Otto, 601XL Calif.

A 2,700cc break in run on a 90% complete airframe: Weekend Double Header, 2nd engine of the year, Rick Koch



7) Operational Data for this combination:

If you would like to read a story about detailed flight data collection on a 2,850cc 750, check out this link: CHT part #5, flight data from Zenith 750 . It is an example of the type of information exchanged on our ‘Zenvair’ group.  If you are attracted to a builders group that is made of intelligent thinking people, you will fit right in with Corvair builders.

If you would like a single example to effectively demonstrate that I am an aviator not a salesman, it is the type of data that I discuss with builders. No salesmen will acknowledge accidents nor difficulties that involved their products, even circumstantially.

Conversely, I am here to teach people what they need to know. I have a long history of writing about subjects that salesmen wouldn’t touch with a 10 foot pole. I write about accidents and friends I have lost, honest mistakes people made and things you can learn from them.  Just about everything know in aviation cost someone dearly to learn. If you are unwilling to talk about these things in plain language, people are doomed to repeat them.


Risk Management, Judgement Error, money in the wrong place. is the story of our only fatal accident in a Corvair powered Zenith. (There is another below, but it was a different company) The NTSB pointed to an incorrectly assembled carb, but read the story and decide if judgment isn’t the root cause.

“If only someone had told him……” is a story about people who don’t listen. Guy A and Guy B were both Zenith 601 builders. Guy B was the passenger in the First 650 accident (AMD airframe- O-200 engine, ruled pilot error). Guy A was a well known and liked Zenith builder and flyer, who quit aviation after this incident.

Risk Management, Factor #1, Judgement. Covers how developing and exercising judgment is paramount to managing your own personal risk.

Risk Management, Experience vs Judgement. Ken Terry was a friend of mine and a huge influence on Grace’s flying, and her development as a pilot. The story is about how experience, even 40,000 hours of it is not a defense compared to exercising good judgment.


Dan Weseman and Dave Dollarhide having a good time at Sun n Fun 2013. They both are in the last story “Friday night” in the link “Three aviation stories”.


 Three Aviation Stories  covers my personal perspective on risk, and what level is worth managing, and how aviators come do deal with this. It speaks of meeting Al Haynes at two points in my life, 14 years and a world of experience apart. It also covers how several members of our EAA chapter each looked at loosing two friends.



Above, A photo taken at Sun n Fun 2006. My wife Grace Ellen and myself, in front of the first Corvair powered Zenith, our own N-1777W. The plane was the first XL model with conventional gear.  Grace is a skilled pilot in her own right. She has been a pilot longer than I have, holds more advanced ratings and owns two aircraft. As a point of ethics, we do not promote, advocate nor sell things we have not personally flown behind.


8) Who is William Wynne?

Modern consumer sales logic dictates that that business should ‘de-personalize’ themselves so consumers find nothing objectionable about the provider while they are spending money.  That model may work elsewhere, and even have advocates experimental aviation, but I don’t buy it.  I contend that Aviation is a different arena, and who you are dealing with, and their ethics, experience and perspective matters.

Building a plane or an engine is a marriage of sorts between the builder and his airframe or engine company. I believe that it is best if everyone goes into it well informed with their eyes wide open. I am always surprised how few people even Google the name of a person they are thinking of working with. You don’t need to see eye to eye with them on every point nor even love them, but the relationship must absolutely have trust and respect operating in both directions. In 25 years I have seen many builders try to justify buying a product from a provider they didn’t really trust. It never works out. It doesn’t matter how good it looks, what it costs or how great it is supposed to work, if it is from a bad guy, it isn’t worth buying.

I could write a quick paragraph about how I am a pilot, a 22 year A&P mechanic, and that I hold both an AS degree in Maintenance and a BS in Professional Aeronautics (accident investigation) From the worlds #1 aeronautical university, Embry-Riddle , but I don’t think that any of that explains my commitment to builders nearly as well as the flying planes of our builders and things we have accomplished. Henry Ford said “A man can not base his reputation on what he says he will do; only what he has done.”

I am plain spoken. to understand why, read the ‘Effective Risk Management’ story below. I have many friends who are experienced aviators who value plain talk. This type of speech also tends to offend people who dabble in aviation and would rather read polite things that align with their pet opinions. I am in aviation to share experience builders need to know, not say things people want to hear. Below are a selection of stories, some humorous, but all with a point, that give people a better understanding of who I am. From there you can decide if you choose to work with me as your engine mentor.


a) Fixing America is going to cost each of us $1.69

b) Greatest Book on Flying Ever Written, (Is your life worth $16?)

c) In defense of plain speaking……

d) Turtles and Cell Phones, 6/24/13.

e) A thought on Easter….

f) Happy Father’s Day William E. Wynne Sr.

g) Effective Risk Management – 2,903 words




9) Notes on trash from Bankrupt LLC’s:

Not all things called a Corvair represent my work or designs. Over the years, our success and willingness to share information has brought out a number of short lived LLC’s that were run by rip off artists, and mentally ill people. Particularly, there have been four businesses that made poor copies of our parts or untested garbage. All of these are bankrupt today. Because they were LLC’s they could take peoples money without any liability to repay it. Today, I have just heard that another is coming back with a new name. The story will never end as long as people don’t do their home work or believe that they are getting a bargain. You can read about one of these companies at this link: Cloudn’t have happened to a nicer guy……

I warn people all the time not to buy things from these people, or to buy this stuff at the flymart. For examples of things no one should have bought, look at this story: Built by William Wynne? Built according to The Manual?

Let me be absolutely clear, that I will be polite to people, but I will not work on, offer advice on, or help with products made by bankrupt people that I considered vermin. If you have one of the engines from these LLC’s you are out of luck. I will not allow you to join our ‘Zenvair’ group nor will I allow you to attend any of the Colleges. This isn’t out of spite, it is to protect these builders lives. They all want to put a band aid on their bad purchase and make it “good enough to fly.” A band aid isn’t going to do it, an amputation is in order. People who blew $12K on Junk don’t want to hear this, they are still looking for a cheap out that doesn’t exist.  I will not assist them in the delusion that they have found one.

The Zenith Builders and flyers website has a small number of old posts from people who bought trash like this for their projects. If you look closely, these people offered great testimonials, but later abandoned their builds. On the same sites, I have builders like Larry Winger and Rich Whittington sharing that the same people took their money and delivered trash. Some people still don’t do their home work.

Corvair Oil System, information on oil pressure gauges.


A friend of ours who is building a Zenith 750 wrote in with a quick note asking about oil pressure gauges and senders. I pulled together this general set of notes on oil pressure measurement and instruments as a good resource on the general subject. Over the years Corvairs have flown with just about every kind of oil pressure instrumentation imaginable. Going back to my point of Principle vs Preference. On this subject, it mostly falls in the category of preference.

The Builders specific question was focused on sending units for electrical gauges, and their reliability. If I had to pick one brand over another, I will say that I have never had an issue with the senders that are used in Autometer gauges. VDO is usually trouble free, but I have personally had one mess up, and it caused a lot of work with it’s erroneous information. Goes without saying, I wouldn’t use one from the land of Chairman Mao.

Some people are concerned about mechanical gauges bringing oil into the cockpit, but in actual experience, I have never had an issue with it. The line itself is 1/8″ on the outside, but only 1/16″ on the inside, and I generally put a #80 hole in a restrictor, at the engine, so even if the line came off, the flow rate is about 1/2 gallon per hour. For the record, I have never seen even the poorest mechanical line installations leak. You can take the nut off at the gauge with the motor running, and it does not “spray” oil, it just oozes, and even when the engine is hot, the oil really isn’t after six feet of line.

Below is the close up of the mechanical oil pressure gauge I have in the Wagabond. In addition to all the other things I like about mechanical gauges, I like the fact the needle covers a 300 degree arc, allowing you to see very fine changes. The gauge below is $54.97 from summit racing.

Auto Meter 5721 - Auto Meter Phantom Analog Gauges

Now get a look at the next part, which is an analog electrical gauge. My primary complaint beyond the fact it is electrical is that this type of gauge is only a 90 degree sweep, making small differences had to see. They also cost about twice as much as mechanical after you get the sending unit. It is priced at $69.97, but the sender is about $40.  I buy Autometer because of the tiny letters at the bottom of the instrument that say “made in USA”

Auto Meter 5727 - Auto Meter Phantom Analog Gauges


For Builders interested in digital instrumentation, Google the name “Dakota Digital”. Below is one of their instruments, but the come in many different varieties, all made in the USA. They have a website you can buy direct from, it has many choices. Just a reminder, never mention to anyone on the phone while ordering from a non aviation company that you are building a plane.  Summit will actually black list you. The people answering the phone have $9/hr. jobs, so don’t jeopardize anyone’s just scraping by living by saying that on the phone, and having them get in hot water for not turning you in. It is an annoying fact of a litigious society, but you are not going to fix it by getting a single mother just above the poverty line fired.

If you would like to read a two part story about the simple panel I built for the Wagabond, get a look at these two following links:


Inexpensive Panel……..part one.


Inexpensive panel…….part two.


If you would like to read a story about Andy Elliott PhD arguing with ww the A&P about instrument choices, look at this one:

“William, you ignorant troglodyte”…….(instrument options)


The story below has comments on oil pressure errors in electronic instrumentation. That part is 2/3rds of the way down at the picture of the Corvair/701.


MGL vs Corvair ignition issue


As you are looking at parts of the oil system, I have reprinted the numbering system of the parts in the oil system for reference here:

Rear oil case group (2000)

2001- Rear oil case casting

2002- Rear oil seal

2003- 5/16 hold down hardware

2004- 3/8 hold down hardware

2005- Case to block gasket

2006- Harmonic balancer

2007- Balancer bolt and washer


Oil pump and regulator group (2100)

2101- Oil pump assembly

2102- Oil pump gaskets

2103- Oil pressure regulator piston

2104- Oil pressure regulator spring

2105- Oil pressure regulator plug

2106- Plug washer


Below is a good article of flight ops with comments on oil pressure indications:


Thoughts on cold weather operation, minimum oil temps, etc.


Below is a short guide on what oil to use:


Notes on Corvair flight engine oils.


Below is a visual reference to where we take the oil pressure on the Corvair engine:


Gold Oil Filter Housing, Standard and Reverse


Below has notes on how the pressure bypass works:


High Volume Oil Pump


Have a pleasant and productive evening.-ww

Corvair CHT, letters and notes.


We picked up several letters from friends on this topic. Let me share some of them and offer a follow up on the story.

Zenith 601XL builder and flyer Ron Lendon wrote:

“And after all that reading I’ll be dipped if I can find your recommendations for the temperature range your followers should be shooting for.  Try putting those details in too, OK?”

Ron, for a guy who made his own cowl and experimented with carbs, I would have guessed that you would have liked reading the information. The topic was the measurement location and test tools, not so much the values. For people with busy schedules and short attention spans, The numbers:

GM Factory limit, measured on bottom of head: = 575F

Highest temp I have personally seen in a Car, measured on bottom, without engine damage = 575F

Highest sustained temp I have personal seen on a CHT in a plane without any damage to the engine = 480F, measured on bottom of engine

Highest temp on bottom of engine  that builders should consider tolerable before stopping to rework cooling system = 420F

A reasonable goal temp in a hard climb that will still have a very wide margin of safety = 380F, measured on bottom of engine, easily achievable with our existing cowls and cooling designs, even in large planes.

Highest Temp that Dan Weseman saw on bottom of engine in full air combat maneuvers in 3100cc “Wicked Cleanex” = 375F

Typical Max climb/ 5 gal/hr cruise temp numbers in well prepped Zenith 601on 80F day = 375F/320F

My target goal, measured on bottom of engine, for gross weight Vx climb in 3000cc Wagabond, 100F day, 5″ inlets, 60mph, 1,600 lbs = 350F.

Lowest cruise temp recorded for a plane with a full cowl, measured on bottom of engine, Chris Smith 3100cc “Son of Cleanex” = well below 300F.

Lowest cruise temp recorded for a plane with a J-3 cowl, Jim Weseman, 3100cc Celibrity biplane = 250F


Above, Phil Maxon’s 601XL, finished in our hangar in 2006, flies over the Atlantic Ocean near Ponce Inlet FL. This aircraft was one of the first 4 Corvair powered Zeniths, yet is has never had any cooling issues. Corvair Cooling, especially on airframes like Zenith XL’s is not a mystery. Anyone who chose to follow our directions and used our designs did not have to be a pioneer. If you want your plane to work, just make it a clone of successful aircraft.


For readers with a little more time, get a look at the following links to stories I have written. I found them all simply by searching “Cowling” , “Cooling”, and “CHT” in the search block at the top right side of this page. If you are only going to read one story for right now, make it the last one, because it highlights the difference between measuring the CHT under the plugs and below the engine:


Cooling with J-3 style cowls. (Pietenpols, Cubs, Biplanes, etc)


Corvair Cooling, Three 2007 examples from our hangar.


Corvair Cooling, something of a human issue…..


Corvair Cooling



Measuring Cylinder Head Temps on Corvairs.


Right here and now I am going to make a very important point: I could put an engine on the run stand, hook up two of the finest CHTs, fuel the engine with pure ethanol free 94 octane gas, have it be ice cold and get ready to start it.  Then I could reset the timing from 30 degrees total to 44 degrees, (a number that people without timing lights often think “sounds good”) Start the engine, and take it to 2,700rpm.

It would take more than 3 minutes for the CHT to exceed 400F on the gauge. Long before this, the detonation would begin, and within 30 seconds of it really knocking, (which would be hard to hear over the prop,) the engine would blow out at least one head gasket, and crush down the ring lands on several pistons.

I could then honestly report “The engine had never exceeded 400F.” I could give many examples like this, and then we could have a lot of internet people offer opinions about the cooling system design we use, and some car guy is going to offer the “expert opinion” that the cowl needs 6″ inlets.  If you want to learn something in aviation, the discussion is going to have to be held at a higher level than that.

CHT is not something that can be discussed as an issues divorced from other operational parameters. I have seen people waste incredible amounts of time trying to solve a “cooling problem” who have not bothered to check any of the basics.

I have been doing this for a long time, and I still have no idea why some people get to the point of having 5 years of work and $30,000 in their aircraft project, but they refuse to drive down to their local auto parts store and buy a $39 timing light.

About a year ago, a guy contacted me who bought an engine I had built for someone else in 2005. He had it ground running on his plane. When I asked him what the timing was set at, he said he had no idea, he just assumed, without a single word to confirm this, that I had set the timing before mailing it to the original owner six or seven years earlier.

I explained that this was a very poor assumption, that even if I had, there is no telling that it wasn’t changed by the first owner, or bumped as it went in or out of the two airframes and was shipped around the country. I pointed out that if I said I unloaded a firearm before selling it to someone else 7 years ago, I would hope that no one would never say to me “I can point it at people today because you unloaded it half a decade and three owners ago.”

About a month ago I heard from the same guy, The engine still was not running evenly on both ignitions but he still had not checked it with a light. If someone presented me an engine that had a years ground running on it, but had never had the timing checked, I am going to flat out say that I would not fly it without tearing it down. Why? because you can check things the easy way with a timing light right away, or you can check things later the hard way with wrenches. Or of course there is the third option, which is just say “I am sure it didn’t hurt anything, It will be alright”

‘Sprint’ builder Joe Goldman wrote:

“William I as am not building my engine I would feel comfortable with 6 cht’ too know what is going on with each cylinder. Does the stock location average temps or would it indicate a particular cylinder over heating. You would not know which one, then how do you locate the trouble.”

Joe, we are friends and you know I think you are great, but lets get a little more thoughtful on this one. First, why are you not building your engine? If the goal of asking me a question is to learn something, then let me offer that building your own engine is the best way to learn many things. Honestly, what are 6 chts going to tell you that 2 are not? Lets say that flying along at 5,000′ and the CHT reads very hot. What are you going to do? Land, that’s what. If your right side CHT indicates an excessive number, please explain to me what knowing if it was #1 #3 or #5 is going to do for you at 5,000′. I have said it many times and many ways, but please know this well; You detect issues in the air, you land. Diagnosis is always done on the ground. The only guy who argues against this is the one who is going to rationalize some reason to keep flying. Each CHT sender cost more tan a Raytech thermometer. If the plane isn’t running right, land and use tools on the ground to look into the problem.

Besides, if you build and equip your engine correctly, you are not going to be flying around looking at issues in the air. Stop for a minute and honestly tell me what is going to happen to an engine, in flight which is going to make an individual cylinder suddenly go up in temp? If you were looking to tell which individual cylinder was causing an issue if your engine started running rough, you are a poor decision maker, and you need a better flight instructor. Any skilled pilot will tell you that the first thing you look for when your aircraft runs rough is the nearest airport. -ww

Cylinder Head Temperature measurement


In this story I would like to address CHT (Cylinder Head Temp) measurement on Corvairs. In the 20+ years I have been working with Corvair flight engines, I have written a great number of informative posts and stories on this topic, and I have also covered this in stories on cooling systems, instrumentation, human factors for lower time pilots and how CHT relates to detonation threshold.

My comments on these topics can be found in our manuals and on both websites. The information we have shared is from personal measurement on several of our own aircraft, dozens of test engines in extensive ground runs, comparative instrumented engines, and a data from a number of experienced Corvair powered pilots Like Dan Weseman and Woody Harris.  All of this has been collected and correlated with my professional A&P perspective, and often discussed at great length with other trained professional aircraft mechanics like Gus Warren and Arnold Holmes, whose experience includes extensive Corvair flight time, in addition to many certified aircraft engines. My data includes many aircraft that worked well, and a handful that didn’t. It is big picture, not myopically gleaned from looking at one or two engines, listening to stories and jumping to a conclusion.

I do not consider myself ‘brilliant’ about this topic. The value of my perspective comes from simple observation of data over a long period of time, working with builders and being in the best position to gather all the data. This is the opposite of just following a few stories that seem to support a pet narrative. Part of what motivates this story is hearing from builders who have been told a number of myths about Corvair CHT info.

One builder was told he “Has to have 6″ air inlets.”   Others have been told that the GM CHT locations don’t work.  None of this is supported by observed data, it is opinion from people who just think their pet theory is right. The myths are not always malicious in origin, but well intentioned and malicious myths are both myths just the same.  Two very prolific sources of this information are people jumping to conclusions based on little experience. If someone has never soloed a Lycoming, Continental nor Corvair powered plane, they can still have an opinion on CHT, it just isn’t worth sharing with builders who need factual, unbiased data.


Above, a Lycoming O-320 (160hp) cylinder that I own.  The 320 is the most respected and prolific light aircraft engine ever built. You are looking at the bottom of the cylinder, the 320 has both the intake port (left) and the exhaust port (right), on the bottom of the head. The arrow points to the CHT probe location. One of the people telling builders his view that under plugs was the only place for CHT obviously didn’t know that all Lycomings use this location, which is very much like the GM Corvair location.  For most Lycomings, the CHT limit is 475F. While I am thought of as a Corvair guy, Our hangar also contains a C-85 and an O-290, and parts of many other aircraft engines. My perspective comes from broad experience and spending time with aviation professionals with far better backgrounds.

A mechanic may be clever with EFI or experienced with vehicles imported from the fatherland, but if they have never turned a wrench on nor flown a Lycoming powered plane, their perspective is myopically limited. I really don’t know a lot about modern car maintenance, but I do know a fair amount about planes, and I know enough about both subjects to say that knowing one does not qualify you in the other.

On the table next to the cylinder is a 50 page Lycoming operations manual. You can down load it for free off Lycomings website. Every aircraft mechanic I know owns a copy and is familiar with the data inside. It is a great book, and even as a Corvair guy you should read it. Quite often, people will say things that are directly against the experience in this manual, even when they are Lycoming owners, speaking of Lycomings. For example, Dan pointed out to me that Lycomings leaning operation in the book is enrich it until it runs slightly rough and lean it only until it runs smooth, exactly the opposite of what most people think. Either you are the kind of builder who is inclined to follow the recommendations of the company that built 300,000 of the engine you are running or you are the kind of guy who is going to follow a story written in Flying magazine by a guy who has never pulled a cylinder off any aircraft engine.

For several years at Oshkosh there was an alternative engine guy who’s background was car racing who liked Gear Driven liquid cooled V-8’s. He started all of his forums by writing on the board “If Lycoming made a car would you drive it?” I spoke with him a number of times and read the stuff he wrote. He absolutely felt he had nothing to learn from Lycoming, (or most other experienced sources for that matter) He doesn’t write that any more. This is because he was killed by a mechanical failure while flying his plane. It was his second major accident. He killed his passenger also. I spoke with him after the first, and I will tell you he learned nothing from it.

 Another person using that same engine wanted to put it back in production, after the accident, but he was killed by a similar engine failure. I just read a nice magazine story about a very nice Australian aircraft using the same gear box. A small postscript at the end of the story said that he was killed by a gear box failure. Same magazine had a press release from a new guy who bought the gear box assets to make more of them. You don’t need a crystal ball to predict the next chapter.

Don’t have anything to learn from Lycoming? They made plenty of successful geared engines like the GO-435, the IGSO-480 and the IGSO-540. No, they didn’t make cars, but evidently being a ‘race car driver’ doesn’t qualify you to make geared engines either. People who claim that they don’t have anything to learn from the successful experience of people who preceded them tend to attract followers with the same mindset. A harmless social phenomenon when the topic is flower arranging, interior design, modern dance or fashionable footwear.  When the topic turns to subjects with consequences, like aviation, builders who plan to die at home in bed with all of their great-grandchildren in the next room, tend to learn from others.


Above, the GM Corvair CHT location. Most common question: “Is it on the same spot on both heads?” Yes, because there is only one head. There is no such thing as a right or left Corvair head until we weld the pipes on the intakes, so this is on “both” heads. In 95 and 110 engines it is threaded 3/8″-16. An easy way to put CHT here is to use a 10MM spark plug ring CHT terminal and hold it down with a 5/8″ long bolt with a washer. This will work great. All Corvairs with the exception of ‘Spider’ and ‘Corsa’  high performance models had an idiot light in the dash that was tripped at 575F by a sender screwed into this hole. I had a guy who had never owned a Corvair tell me that the 10mm ring would not work because “it needed to touch the bottom of the hole” Really? the GM sending unit didn’t, and it read just the same.

For another view of a Corvair powered plane that is slow climbing, but runs cool, read this story: Gary Burdett, 2,850cc Zenith 750, now flying. (engine selection)  I personally verified the temps that Gary is getting by independently measuring them in person, on his plane, at Corvair College #26.  I heard from a guy who said he didn’t think it could run that cool, that both Gary’s instrumentation and mine must both be wrong. This comment came from a person who has never seen the plane nor the engine, has no idea where the temps were taken from, nor does he have a running engine nor a pilot’s license, yet he is still quite sure he is correct, unwilling to even entertain the possibility he is wrong. Some people you are just not going to reach, and that is OK. Plenty of people who stayed on land back in Spain felt that if Columbus had just sailed a little further, he would have fallen off the earth, and nothing Columbus did was going to change their minds.

Above, an eight year old photo from the old hangar in Edgewater. In the foreground, my 1966 140HP four carb Corsa, behind it Kevin’s 1965 180HP turbo Corsa. Both of these cars have factory CHT gauges. The factory turbo cars did not use a waste gate, they just had an oversized turbo and a very specific muffler, and the result was a very simple system that did not go into boost until the car had some serious rpm, the throttle mostly open and the CHT over 400F. Below this, the head dissipates the heat energy the turbo needs to make boost. The engine will not make its full output until it is up in the 500F range. Granted, they didn’t have to run this way for a hour at a time, but I have met people who don’t believe that Corvair engines were run that hot in the cars without damage. They hold this opinion even though they have never driven a turbo Corvair and seen the CHT gauge with their own eyes. I have driven 120,000 miles spread over the 4 Corvairs I have owned. At the time the Photo was taken, Kevin owned 7 other Corvairs, Grace had her 65 van, Gus had a ’67 Monza and Dave had a ’69 Monza. I felt that our ‘hangar gang’ was qualified to comment on Corvair operation.  I have met many people who have never owned a Corvair with strong, but incorrect opinions about how the engines ran in cars. Explaining the basis of my observed experience to the contrary, they often stick to their opinion, they are more comfortable with any antic dote  that seems support their opinion than a mountain of contrary evidence. This is especially true if the person in question is a car mechanic.

Corsa models, (140 and 180 HP) have the hole threaded 3/8″-24, same as a Lycoming. To make the 95 heads on my plane compatible with standard Lycoming probes, I have helicoiled them for 3/8″-24 threads. The probes I am using are Electronics International P-101s with A-101 quick detach fittings. They are in the Aircraft Spruce catalog on page 523.


If a guy wants to share an opinion about temp measurement that is contrary to mine, it might be worth asking what kind of test equipment he us using. If he looks at the head of an engine he did not see run and wants to jump to a conclusion, or he wants to use internet data from a builder who never set the timing with a light or is running a non aircraft carb, it probably isn’t going to be as accurate as I can collect in person.

From my tool box, top row, Fluke two channel digital type K temp meter, accurate to less than 1/2% of reading, compares two probes simultaneously, reads all common aircraft probes. Digital type K contact thermometer, 0-1,200F, accurate to 1 degree. Westach CHT, common in aircraft, not accurate source of info, but commonly quoted on net. Bottom, two Raytech non-contact thermometers. accuracy limited to surfaces that don’t have shiny finish, tends to read too high in many circumstances. OK for quick check looking for cold cylinder, but weak on data gathering. Small spark plug item: Original AC thermistor from 140/180 HP Corvair. Same part actually used on many certified aircraft such as Twin Comanche.


Above, the instrument panel in our Wagabond, in the process of being wired. The gauge in the lower right is the CHT. It is a very accurate military unit with a little stamp on the back that says “Calibrated MCAS Cherry Point.” It takes type K thermocouples and need no power at all to read, it is independent of the electrical system of the plane. There is a hole under the gauge for a left /right switch.

I like traditional gauges, and 2 CHT’s in the stock location make sense to me. You can also run 2 CHT’s in the stock location with many Glass Cockpit displays. If you want to run 6 CHT’s, then you are probably going to run them under the plugs. If you do this, know that we have gathered plenty of data to say that these will actually run hotter than the CHTs in the GM location because they actually read the temp of the plug as much as the temp of the head. They can be a little pain during a plug change, and if you are not careful, you can over torque one in a plug hole with a helicoil or a time sert in it, and the sending unit will stick to the top of the thread and extract it when you unscrew the plug.  One way to avoid this is to run a copper washer, then the sender, then the plug, but this is even more likely to show the temp of the plug. I have wired plent of planes for 6 CHTs, I am not enough of a zealot about it to really care about what other people would like in their planes. Dan has 6 CHT’s under the plugs in the Panther and it works great.

In general, the plug temp on #1 will read 60-80F higher in climb that the same cylinder with a probe simaltainiously  running on the bottom of the head. If anyone is speaking of CHT’s on a Corvair, and anyone comments on it without first establishing where the temp was taken and what kind of gauge was used, then they are not adding anything to the discussion. Quite often, if a builder mentions that their plane runs hotter than they would like, the first thing people like to chime in with is that there must be something wrong with the way we teach people to build cowls and cooling systems. In reality, we have people who are flying the same system successfully, so logic say to check these this first:

1) Is the timing set correctly with a light?

2) If there is a significant  L/R difference, especially at part throttle, and it has a flat slide carb like an aerocarb, Elison or a Rotec, it is the carb causing this effect. Butterfly style aircraft carbs don’t do this.

3) Does the cowl have inlet rings?

4) Does the outlet have a lip on it and is it 3X the size of the inlets?

5) Is the instrumentation correct?

6) Are they the correct spark plugs?

7) Is the fuel high enough octane?

8) is it a one of a kind prop? (these frequently don’t pump much air down near the inlets)

The above 8 points are the most common factors that keep the engine from running as cool as possible. Be advised that I have seen people break all 8 at the same time and still fly their plane without overheating it. God protects children and usually fools also. If you like the image of being 100 and meeting your great-grandchildren, I suggest not trying to discover the exact statistical value of “Usually.”  -ww

3,000 vs 3,100 cc Corvair engines.


A number of builders just getting into Covairs miss the distinction between these two engines. Below I have a number of links to illustrate the difference, but in a nutshell, the 3,100 was the “big bore” option on corvairs between 1998-2008. It has since been largely superseded by the 3,000 cc Corvair with good reason.  There are still a number of 3,100s flying, and there will be for a long time, but very few, if any new ones are being built these days. A number of builders who previously flew 3,100s have elected to build a 3,000 as their next engine. There are reasons for this, and I will detail them below.

Above, the 3,000 cc Corvair that is flying in the Panther prototype. Notably, Dan Weseman successfully put several hundred hard hours on his 3,100cc engine in his “Wicked Cleanex, ” but opted for an all-out 3,000 cc Corvair in his aerobatic Panther. The engine both cary the same 120hp rating, but the internal differences make the 3,000 more durable, and it is far easier to build.

On the surface, the difference between a 3,000 and a 3,100 is simple: the 3,000 has a 92mm bore and the 3,100 has a 94mm bore. But the details go far deeper. The 3100 was originally developed for dune buggy’s in California, and piston/rod cylinder kits were sold by a number of companies in California. I bought one from Bob Sutcliffe in 1998, and his quality was good.  At early Corvair colleges we assembled at least 15 and perhaps as many as 20 of these engines. It was very apparent that the quality of the kits varied a lot. The other issue was that builders who knew nothing about engines spent lots of money on poor kits from California, and them brought them to Colleges and said “I just spent $5,400 with a dune buggy place that has never seen an airplane, and now I would like you to build this for me for free this weekend.”

The main problem with this was several fold, first, ‘free work’ isn’t what colleges are about; second, these engine required a lot of hand work and fitting to even be assembled. Often they had no standardization, and individual pistons and cylinders could only occupy specific locations on engines. The big one was that each of these engines required a custom set of pushrods to be made so the valve geometry was correct. We and others like Mark Langford repeatedly told people that this was not a first engine to build. Most people listened, but there was a certain type of person that just wanted a bigger engine although they were unwilling to learn the required detailed information to understand and assemble it.

Internally, the 3100 had many VW 94mm parts in it. Here are the things about that that I didn’t like: The pistons, even good ones made by Mahle, were cast. The VW wrist pin is 22mm, and the dune buggy mentality was to just bore out the Corvair’s .800″ (20mm) rod to take the larger pin and run it as a steel on steel no bushing floating pin. This worked, but was a poor way to do it. The California companies would occasionally send out a rod with a .060″ wall thickness around the pin and think nothing of it. These engines also had the head gasket cut so large that it broke into the upper head bolt areas. Using the VW pistons made the compression height wrong for the Corvair, requiring custom pushrods to correct it. The Compression on these engines was really too high to safely have Mr. average pilot run car gas in it. Many of the people attracted to them didn’t recognize that Mr. average pilot was a polite name for them. If you would like to read about 3100s that worked well, look at:

KR-2S at 700 Hours – Joe Horton


Zenith 601XL-3100cc Dr. Andy Elliott


Above is the 3100 of Dan Weseman in the Cleanex. This engine and the one in Chris Smith’s ‘son of cleanex went on to log about 500 hours each. Note the reverse gold oil filter housing on the engine. Have a look at four 3100s taking off in a row from Corvair College#16 in South Carolina, Langford, Weseman, Smith and Horton:


The first Correction actually came from Brady McCormick, Owner of the now defunct Magnificent Machine.  What Brady did was have a new forged piston made in 94mm. This was a good idea, and he incorporated the Corvairs deck height and pin diameter in his design, automatically correcting the geometry. But it still had the head gasket issue, and the piston design Brady chose was a light weight one for high rpm engines. It’s compression was still high, and It could not tolerate having a dish machined in it. Still it was an improvement, and perhaps 15 engines were built this way. Examples would be Jim and Rhonda Wesemans Celebrity; Mike Robitie’s Cleanex engine;( Guest writer: Phil Maxson, flying a 3100cc Corvair in his 601XL ) and several production engines we built like this one:

Brady’s pistons are no longer available, and the forging blanks they were made from have been acquired by Clark’s Corvairs as the basis for their USA made forged pistions. (They are only made to .060″ over bore now, and 94mm is a .264″ overbore)

Above Jim and Rhonda at CC#23, with Dan in the cockpit. the engine in this plane is a one of a kind reverse rotation Corvair, a 3100 with Brady pistons. Jim is a life long professional aircraft mechanic by trade, and a very clever guy. He had the experience to create a very unique Corvair for his plane. Most builders are far better off building an engine that is a regular “bolt together” experience. Jim and Dan developed their 5th bearing as a father/son team. Jim and Rhonda make Corvair cowling and baffling kits, but they made their best contribution to experimental aviation back in 1975…by having Dan. 



The actual permanent solution was having a better forged piston made, and reducing the bore to 92mm. In doing this we went to a different American manufacturer that specialized in pistons with thicker crowns that could have a dish milled in them. Below is a look at the 3,000cc piston top in a bore along with the head is designed to match.

Above, a 92mm/ 3,000cc Corvair set up. This is the final evolution of the big bore Corvair for aircraft use. Note how the head gaskets don’t break into the stud holes. The flat area on the head and piston are referred to as “the Quench”. There come very close to each other, making the charge burn much quicker with much less chance of detonation. The dish in the piston keeps the static compression low, ideal for running on car gas or 100LL.

The 3,000 cc engine is a far better engine for builders to work with. Although I can build any Corvair engine I like, and our 601XL had a very strong 3,100 in it, I didn’t hesitate for a second to switch to a 3,000 cc engine for our Wagabond. People who only know a little bit about engines often think that loosing 100cc is going backward, but in reality I typically de-tuned our 3100 because it had cast pistons and what I considered excessive compression. On the Wagabond’s 3,000 cc engine I am setting up to run at full power for as long as I like without having to retard the timing for car gas operation. Let this serve as a basic introduction to how the 3,000 cc engine has surpassed the 3,100 as the dominant big bore Corvair flight engine. For more 3,000 cc stories follow the links below.-ww


World’s Strongest 3,000cc Corvair, built by Greg Crouchley


Panther Prototype Engine 3,000 cc/120 hp to OSH


3,000cc Engine Running


Getting Started in 2013, Part #16, 3,000 cc Piston/cylinder kits


Flying Zenith 750 w/3000cc Corvair, Doug Stevenson, California


3,000cc/Billet Crank Shortblock, Destination: Waiex


New 3,000 cc Cleanex, Dale Williams, SC


Corvair vs O-200…. weight comparison


A Zenith 701 builder that I spoke with at the open house wrote me a short note asking some questions about the weight comparison between these two engines. This is something I have directly compared, something we have very good data on, and some valid and useful commentary.

For people with short attention spans, I will cut to the chase and say that a modern Corvair, as we teach people to build them, with electric start and a charging system, weighs the same installed as a standard O-200 Continental. You can see in the photo below that I have weighed, thrust tested and dyno run them side by side personally. Many people will comment on the subject of engine output and weight on power plants they have never laid a hand on, far less run on a dyno. Most of the “evidence” people present is well intentioned, but erroneous just the same. Bad data, presented with good intentions or malicious ones, is still bad data. The numbers here come from personal measurement, intentionally done in public for people to see.

“More Lies are told in experimental aviation than in singles bars” is a saying I made up 15 years ago to illustrate the loose association with truth that many people in our field have. The most common fib told in home building is under  quoting how much something weighs. (This is ironic, because compared to numbers like HP output, true stall peed, or ultimate G strength, the weight of anything is a very simple matter to check, but very few people ever do.) Many people I quick to point the finger at salesmen, but let me also say that I have done the weight and balance on something like 100 homebuilt aircraft, and only found 10% of the owners were remotely telling the truth on their W&B sheet. Many of these people told their buddies their plane was exactly 100 pounds lighter than is was. Frequently they repeated it often enough that they forgot they made it up, and could have passed a polygraph test swearing to it. Take this away: Don’t believe anything you hear about weights unless you are listening to the guy who did it himself, who has photo documentation of him doing it. If you would like to read a funny story about how reality has a hard time competing with fantasy, take a moment to read this link:

Unicorns vs Ponies.

On the left above is the Continental O-200 as removed from a 1959 Cessna 150. This engine is considered the standard  against which all other 100hp class engines are measured. It is a direct drive 4-stroke, 4-cylinder engine of  200cid. It carries a horsepower rating of 100 at 2,750rpm. I have read that Continental produced about 50,000  O-200s. On the right is a 170cid Corvair engine. For size comparison, the O-200 is 32″ wide without the baffling.  The Corvair is 28″ wide.


The caption in italics above is actually nine years old from our main page It is from a long test series on dyno and thrust testing the O-200. You can read the full story at this link: . The picture above shows that a Corvair is smaller physically than an O-200. Let me also offer that I know a bit about Continentals and I like them. Graces Taylorcraft has an STC’ed C-85-12 in it, an engine that is nearly Identical to an O-200 in physical size and weight. Keep in mind that when people compare engine weights on the net, very few of these people have owned both of the engines they are commenting on, and in many cases, the guy offering the data has owned neither. It doesn’t make then bad nor evil, it just means their data on this subject probably isn’t good.

What about the often quoted 188 pound weight for an O-200? That is erroneous, as it does not include the starter, mags, plugs, carb, oil, or many other items it takes to run the engine. The data was actually presented that way so if a manufacturer chose Eisman mags instead of Bendix, he could do a weight and balance engineering solution on the engine. The 188 number was never meant to be a comparison all up weight.

What about the new light weight O-200? Yes, it is lighter than a traditional model, by as much as 20 pounds. But this engine, which Continental rep. Kim Winner brought to the Zenith open house, sells for $20,000. It is new, and they have made very few of them, and you are not likey to come across one for sale used for another 20 years. Many of the parts in it can not be used on older engines. Most builders are taking about a Corvair they could build on a $8500 budget vs a traditional O-200 taken from a Cessna 150 for roughly the same money. If you want to spend $20K, I can build you a Corvair that is far lighter than the lightest O-200 ever made. Given $8,000 or $10,000 just to spend on weight reduction, much could be accomplished, but that isn’t an engine most people are considering, and neither is the new light weight O-200.

Is an O-200 ‘Approved’ for a 701 but not a Corvair? You can call Zenith and speak with Roger or Sebastien, and I am sure that they would advise any 701 builder to first consider lighter engines. But they would also tell you that both engines have powered 701s before. We bought our 701 test bed kit directly from the factory in 2005 and completed it in 2007.  Sebastien sold it to us to test the concept after seeing the success of our 601/Corvair program. The 701 worked. we made no attempt to lighten the Corvair for it, and the plane weighed 677 pounds ready to fly. (if that didn’t sound very light compared to other numbers you have read on the net, go back and read Unicorns vs Ponies again.) It did not need any ballast whatsoever to get into the CG envelope. On this last point, the Corvair has a distinct advantage over the O-200; The Corvair is ‘flat’ on the back, and can be pulled right back to the firewall without creating a maintenance issue. An O-200 has the mags and wires sticking out the back, and they require several more inches of clearance to be removed without the requirement of pulling the engine off the mount. Although the Corvair and the O-200 effectively weigh the same, you can’t get the O-200’s CG nearly as close to the firewall. It may require ballast just to get into the front of the CG range.


Above, Our test bed Corvair powered 701 in the Zenith booth at Sun n Fun 2010.


I have heard that a heavy engine can break the 701 nose gear, truth? Yes, a very heavy engine could be a factor, but when we built our 701 I studied this closely, and a far bigger issue was people flying the plane forward of the published CG envelope. One guy had tried a Geo engine with a belt drive on a 701. This was actually lighter than a Corvair, but the engine layout was very long, and it had to be positioned well forward to clear items from the firewall end of the engine. The result was I guy flying around 2″ ahead of the forward CG limit. The plane could be landed smoothly by rolling it on at 60 mph, but that wasn’t the point of the 701. When the Geo guy tried landing slow and pitched the nose up, he found out that planes that are ahead of the forward CG limit drop their nose like a rock at high angle of attack. This is the effect that harms the plane. It is actually a CG issue, not a weight driven one. Poor pilot technique is another big factor. Any guy willing to get a little time in type training and fly within the published CG range has little to worry about.

What about reasonable cost Corvair modifications to reduce weight? A 3,000 cc Corvair actually weigh 7 pounds less than standard ones becase the bigger engine uses a lighter aftermarket cylinder set. A billet crank is nearly 4 pounds lighter than a stock one. A welded pan is a pound lighter than a billet one., etc. There is a list of parts than can get 15 pounds off a Corvair, but most builders find the engine to be acceptably light in the basic form. People frequently ask about putting aluminum cylinders on Corvairs. I have been working with Corvairs for 25 years, people have been talking about these for at least 12 years, and yet no one has ever taken a set flying. I have good reason to doubt the would work.  If some one tries to talk you into anything that has never flown, and the national expert doubts will work, realize they want you to be a guinea pig.  They sell down at the pet store for $20, and if your life is worth more than that, don’t be anyone’s Guinea pig.

Last Comment of weights: Two people in the alternative engine game, myself and Robert Helms, president of UL power, never hesitate to tell the truth about how much our respective engines weigh. Robert has nothing to loose by doing so; He has the lightest engine on the market, he doesn’t need to embellish the facts. In my case I don’t have anything to gain by under reporting the weight of a Corvair. People choose the Corvair because it is affordable, smooth, a learning experience, well supported, made in America and a multitude of other reasons. It has the features above, while having an acceptable level of weight for a broad variety of aircraft. If I fibbed about the weight of the engine I wouldn’t attract any significant amount of new builders, but it would undermine the trust and rapport with builders we already have in place.-ww.


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