Mechanical Fuel Injection Testing
One of the things that we have been testing lately is a mechanical fuel injection system from Precision, makers of certified aircraft fuel systems.
Precision has developed a single point fuel injection system that is entirely mechanical for engines in the Corvair’s power category. We have had one of these for several months and conducted a number of tests. Below is a quick outline of some of the data we’re collecting.
Above on the left is the Precision fuel injector, on the right for size comparison is an MA3-SPA Marvel Schebler carburetor, the most popular Corvair carburetor. The Precision injector is designed to fit in exactly the same space with the same bolt pattern as an MA3.
Just for starters, let me say that many people do not understand the function of mechanical fuel injectors on aircraft. The above unit is closely related to the operation of an RSA fuel injection system, the gold standard of mechanical fuel injectors. Part of what confuses experimental aircraft builders is the fact that there are a number of carburetors that include in their name the misnomer “throttle body injector” or “Aero injector.” Both the Ellison and the Aerocarb are useful carburetors but in no way shape or form are they fuel injectors. They are simply flat slide carburetors that do not have float bowls.
The defining characteristic differentiating a mechanical fuel injection system and any other type of carburetor is simply that the mechanical fuel injector meters off density, not off volume. Anything that meters fuel off the volume of air flow that comes through the throttle is a carburetor. Such systems will always change their air/fuel ratio as the density of air changes. Conversely, mechanical fuel injectors, such as the Precision unit, meter off density. When they are set to a specific air fuel ratio they hold it, no matter what altitude you climb to, nor how the conditions change. If you look closely, there are four chambers on the diaphragm of the Precision unit. These four chambers allow this to function as a very precise pressure regulator and metering device based on the mass flow of the air passing through the assembly.
To give you some idea of the quality of this unit, and its adaptability to different airframes, the directions actually spell out that it can be run on any fuel pressure unregulated between 20 and 80 PSI, and it will handle momentary over pressures to 180 PSI without damage. Because of the diaphragm assembly, the pressure can actually fluctuate between any of these pressures and it will not change the air/fuel ratio.
The primary difference between the Precision system, and typical certified aircraft systems, is that this is a single point injector that does not have injector nozzles in the intake ports. It has one nozzle that is in the body of the unit after the throttle plate. This unit is immune to carburetor icing. Yet in operation the fact that the fuel is vaporizing 18 inches upstream of the intake ports allows a very significant evaporative cooling effect. Unique to this unit is the fact that it is equipped with a very potent accelerator pump that gives it instantaneous throttle response that one associates with port fuel injection.
Above, the Precision injector mounted on a 3,000 cc Corvair on our engine test stand. Bolting on the injector in the place of our typical MA3 only took 30 minutes. Even the throttle arms are in the same location. As far as I know, this is the first mechanical fuel injection system that has ever been used on a Corvair engine turning a propeller.
The system is not cheap. Its suggested retail price is more than $2500. If you are building a Pietenpol and were planning on using a Stromberg, you’re probably not going to change plans and pick up one of these injectors. However let’s look at this from a different perspective. People who are spending $18,000-$20,000 to buy a Rotax 912 or a Jabaru 3300 will find that their engines are equipped with one or two Bing motorcycle carburetors. Although these carburetors are allegedly altitude compensating, in practice they are far from it. You can ask any operator of a Jabiru engine and they will tell you that at high power settings and high altitudes, their engines are very thirsty, and they have no way to compensate for this. These expensive buy-it-a-box engines come with Bing carburetors because they are cheap.
Now let’s look at the 3 L Corvair engine with the injector above. It is the most expensive Corvair powerplant I have built in the past couple of years; the price of the engine complete without the fuel injection on it is $11,500. At $14,000, it is $4000-$6000 less expensive than imported engines fed by motorcycle carburetors. Combine this with the Corvair’s made in America pedigree, and its reputation as tough as nails, and many people find that it’s a choice they’re interested in. Corvairs are not for everybody. Most people don’t actually care where their products are made, or if they will be serviceable in five years. It’s a free world and those people can find engines that suit their needs. For people with different value systems, I am glad to conduct R&D to find out what is a real value in high-end engines.
Above, the engine runs on the stand in front of our hangar. The fuel line leads down to a rack of instrumentation, a high-pressure pump, and an external pressure regulator used for testing purposes. The engine ran very smoothly, and passed our early tests. I will have the unit on display and more information in our NO34 booth outside Building C at Sun N Fun all week.
Schwartz Engine Runs at CC #22
Above at left with me is Blaine Schwartz of Texas, a Zenith 750 builder who assembled his 2850 cc, Roy bearing equipped engine with Falcon heads at Corvair College #22. In this photo, we hold Blaine’s license plate displaying that he is a devout Chevrolet fan. 10 years ago, General Motors put up billboard advertisements with pictures of red Chevrolet Corvettes. The only caption they put on the bottom of the sign was big print that said “They don’t write songs about Volvos.” Building Corvairs is part of my lifelong admiration and passion for Detroit engines.
The above photo shows where Blaine started midmorning on Saturday. Roy shipped the case already assembled with his bearing on it with the crank and cam in it. This is how he delivers his product to builders. This is why at first glance it appears to be substantially more expensive than the parts to build a Weseman bearing engine. Blaine found it a good value and worth the wait to get a running start at his engine. This assembly from Roy is completely compatible with all of the products that we sell and directly works with Falcon heads.
In the above photo I am demonstrating to Blaine the use of my Snap-On electronic torque wrench on the rod bolts.
An overhead view showing the Pistons and Cylinders installed. Blaine’s engine is a 2850 cc powerplant, utilizing a Piston and Cylinder Set from us. The cylinders used in the Kit are Clark’s full fin heavy duty cylinders, bored .105” oversize.Clark’s does this boring for us on their very accurate machinery.
In the above photo, I use a soft rubber mallet to tap on Blaine’s Gold Prop Hub. Engines equipped with Roy’s fifth bearing use a Short Gold Prop Hub.
The above position, with the engine standing on its nose, is my preferred position in which to set the valves. This photo also gives a good view of the full fin heavy duty cylinders from Clark’s that are part of our 2850 cc Piston Kit.
Above we are bolting on the Front Starter and giving it a good look before taking the engine outside to fire it up on the ramp.
30 hours later the engine is on the test stand ready for its run on Sunday afternoon. We utilized the engine to teach many people the assembly and priming sequence and how to install a Distributor.
Above, Blaine’s engine a few minutes into its test run. We did a full 30 minute break in on the engine with the RPM between 1800 and 2200. The engine ran flawlessly. Hats off to Blaine, John and Becky for running their engines at Corvair College #22.
Franklin Engine Runs at CC ##22 KGTU Spring Break 2012
Above, Grace, John Franklin and his new running 2700 cc Corvair powerplant. John worked on this engine at Corvair College #21, and finished it at CC #22. It is a smooth running powerplant that features a simple stock oil system and no fifth bearing. This is a good example of the baseline economical powerplant headed to a Pietenpol. If John chooses, he may later upgrade to a Weseman bearing or any of our Gold System Parts without a major rework on the engine. This engine has a nice set of Falcon heads on it and a first-class nitrided crankshaft.
Above, Kevin Purtee, Guy Bowen and Greg Crouchley surround John’s engine after it is placed on the run stand. We primed the engine with an electric drill for a long time with the valve covers off to make sure that the lifters all flowed oil before we ran the engine. Because it was cold, one of the lifters was very reluctant to flow oil. After the test run, we brought the engine back inside, cracked open the valve cover, and confirmed that warming the oil and the test run had gotten the system to flow plenty of oil. When you build up the engine yourself, you have the confidence to look into things like this and verify that it is to your satisfaction. Building a Corvair is about building your own skills and getting away from being beholden to mechanics, engine distributors and importers. Real freedom is knowing that you can count on yourself.
Above, John and I check the oil flow on the engine.
During the assembly phase we went over a number of details, including instrumentation. While we do have some very high-end showpieces at the Colleges, the events are still largely about rank-and-file builders building powerplants that will serve their individual needs. I always encourage people to build the best powerplant they can afford, but the Colleges are about educating people to judiciously apply the money in their budget to get the maximum effect for it.
At Colleges, you will have plenty of help for any task at hand. This was the real spirit that all aviation events were supposed to have but many are sadly lacking. I can’t fix the rest of the world, but Corvair College will always have the spirit of camaraderie and friendship between aviators that has always been a central part of good aviation events.
John’s engine ran after dinner on Saturday night, and he had many fellow builders to cheer on his achievement. It was chilly and wet out, but John didn’t seem to mind at all.
A milestone event in the building experience: Your engine runs for the first time. John shares a few words over the sound of the powerplant with Grace.
Above, John’s engine, a good example of a baseline Corvair powerplant. Notice its stock oil system, including a 12-plate cooler. Internally, however, this engine is built of first-class components. If John chooses later upgrades, he will not have to do anything internal to the engine as the upgrades will bolt on externally. He made some good choices about quality components internally where it would be difficult to go back and upgrade, while leaving open the possibility of a Weseman bearing or further evolved oil system. A Corvair engine like the one above has approximately $4000 in parts in it. There will always be people who would rather buy a C-85 without logs out of the flymart for the same kind of money no matter how many times I point out that a quality C-85 does not need to be dragged all the way to Oshkosh to be sold for $5000 (only the bad ones have to be transported that far and sold anonymously), some people will still try to get away with such an alleged bargain. That’s their choice; they aren’t in experimental aviation to learn things, they’re here to try to get away with stuff. Conversely, a guy like John has put in some real work, learned a whole lot of stuff, and has an engine that is internally new and well proven for the task ahead of it. It also comes with all of our support and the camaraderie of Colleges. Not everyone values such things, but for those who do, we have plenty more Colleges lined up and I will be in this for as long as I live.
After verifying the oil flow in John’s engine, we took it back out and ran it again just for the heck of it. It sounded great, and he was very proud of building it, as well he should be.
Shipman Engine at CC#22
Above is a look at Becky Shipman’s engine before I finished the assembly. Notice that the fins extend all the way around the head studs. These are 1960 Corvair cylinders machined 1/16 inch over bore. This makes them standard bore for a 1961 to ’69 Corvair. After carefully machining a notch in the bottom of the cylinders, it is possible to mate them to a set of 1964 heads and a long stroke crankshaft. This combination produces one of the lightest Corvair engines without resorting to unreliable or unproven components. Although these cylinders have more fins on them than standard 1964-69 cylinders, the fins themselves are thinner in cross-section and the cylinders are lighter. 1964 heads are about 1 1/2 pounds lighter each than ’66 and later heads. A number of small details like this when watched closely add up to an engine that is approximately 10 pounds lighter than typical Corvair powerplants. The cylinder heads on this engine were prepped for me by Falcon. A close look shows that the pistons in the engine are Sealed Power products with coated skirts. This particular set was made in the U.S.A. before production was corporately outsourced to India. Connecting rod bolts in the engine are ARP. The valves on the engine are one piece stainless with rotators on the exhausts.
Above is a view of the engine complete with its Gold System Components installed and prepped for a test run. I broke in the engine for approximately an hour before we brought it to the College for a further run and delivery to Becky Shipman. This view shows how thin 1960 fins are by looking at the upper stud on the number five cylinder. This engine is equipped with a Weseman bearing fed by the silver braided oil line leading directly from the Gold Oil Filter Housing to the bearing behind the Ring Gear. It has the inboard section of its front Alternator Bracket installed, the gold corner of which is just barely visible. I rarely install a charging system on an engine while we are doing the break-in on the engine stand, but it is far easier to install the inboard bracket before the ring gear and the Prop Hub are in place.
Above, I stand with Becky and her running engine at the College in Texas. The engine is destined to be installed in her Zenith 650 airframe. Becky drove all the way down from Minnesota to attend the College and pick up as much technical information as possible as well as bring the engine home. Her teenage son Kyle also came down from Minnesota. He proved to be a very sharp student himself and has plans to attend the Air Force Academy.
Becky is an Ivy League trained PhD engineer who works in manufacturing for 3M company. She has a good mechanical background and a significant amount of flight experience. I am always glad to work with any builder who shows a genuine interest in learning about the engine they will be operating.
Another view of the engine during an extended run on Saturday.
After the run, the engine was brought inside, allowed to cool off and removed from the test stand so that John Franklin’s engine could be run next. At Colleges, there’s always a lot of helping hands for any task to be taken care of.
Above is another view of the same engine running in our yard in Florida. The test stand is chained down to a giant concrete block in the ground. Our neighbor Wayne, an aviator of long experience, stands next to me and enjoys the smooth sound of Corvair power.Wayneis six months away from 80 years of age, yet he is an active IA, and flies his Wittman Tailwind and RV-7 every chance he gets. I have heard many men 20 years younger than Wayne talk about not going after their dreams in aviation because they felt too old. Probably something of a self-fulfilling prophecy. Wayne never goes for such negative thinking. He constantly is working to enjoy the day at hand. Anyone attributing Wayne’s energy and longevity to clean living would do well to look closely and notice the beer can in his hand. He grew up on a rural farm in South Carolina that did not have running water, went on to raise several children as a single parent, served in the military and later as a Fire Chief in Jacksonville, has owned, built and flown a wide variety of aircraft. The common thread through his entire life experience is his outstanding positive attitude.
Here is a brief film of Becky running her engine at the College:
What is a core engine worth?
This question just came up because a guy thinking about building an aircraft engine asked it after seeing several listed on Ebay, one for over $1200. I went and looked because I thought he might have slipped a decimal place. He didn’t. One guy in South Carolina is selling several Corvair engines, listed as aircraft engine cores for very, very high prices. I don’t know the seller, because in the wonderful world of Ebay he is identified only by the email address “H20less”.
It is a free world, and people are allowed to try to sell anything they want, for what ever price they think they can get. I am not angry at the guy for trying, and neither should ‘H20less” be angry at me for telling builders that they are not worth anywhere near what he is asking. At least when I express this opinion, you get to know who is saying it.
I don’t care how much people sell other things on Ebay for, it isn’t my concern. The reason why this is an issue is two-fold, first I treat people building Corvair flight engines as if they are friends of mine. We run a business, but it isn’t aimed at seeing how much money we can take from people at an auction, it is just aimed at teaching people how to build engines and selling them the parts to do this at a good value. Every single person with a running Corvair aircraft engine would tell anyone about to pay $1200 for a core, or $450 for that matter, that they are about to spend way too much money. The second issue I have is that a guy like this has a vested interest in justifying his price by creating the impression that these engines are hard to find, which they are not. As evidence that they are still easy to find, reading the ad closely, it states that he just bought all of these engines and is reselling them. That tells you they can be found, and I am sure he paid a lot closer to the realistic core value of $150-$250. We still have lots of builders who buy their core for $100.
The place where most builders find their core today is Craigslist. If you don’t know how this works, google search the term and look at the city near you and search the word Corvair. Craigslist is a giant on-line service that works just like the classified ads in newspapers. It is localized, because you don’t really need to know that a guy in Auckland NZ is selling something that a guy 30 miles away is also selling. It isn’t a game like auction of hidden prices like Ebay either.It is just ads for people selling things. The best part is that you can run an ad stating what you are looking for, people in your area will read it and contact you. This second method is how 50% of the builders who got started last year picked up their core. I polled them at Oshkosh last year, and the average price they paid was less than $100. For all we know, they guy selling the stuff on Ebay used Craigslist to buy it. Ask any of your friends if they have bought things on Craigslist and you may be suprised who much stuff is sold there. I bought our trailer, my motorcycle and many Corvair engines off Craigslist. The cost of each of these was far below the loest price I had ever seen any of them sell for on Ebay. One more thing, Craigslist is free. If you’re looking at a core, a conversion manual and a disassembly DVD from us are good tools. Even if your yet to get these, you can still write me and ask about a core you are looking at. I will gladly answer, because I don’t want to have any builder, a person who I regard as a friend, get started off on the wrong foot by paying way to much for a core engine. – William
3,000cc Engine Running
Below is a freshly built 3,000cc Corvair running in front of our hangar. We built it for Zenith CH-750 builder Lary Hatfield. Grace and I met Lary and his sons at the 2011 Zenith Open House in Mexico, Missouri. The Hatfields were taking the Zenith Builders Workshop and picking up their airframe kit. They got a good look at all the engine options for the aircraft, considered carefully and selected the Corvair. Lary acknowledged that each of the engine options for the 750 had some appeal, but our knowledge of the engine, our 23 years in the business, the number of Zeniths flying on the Corvair, and the fundamental simplicity of our approach made the decision for him.
The economic appeal of the engine that attracts many people was not a factor. Lary speaks with a lot of fatherly pride about his sons’ hard work ethics and their personal successes. Although he never mentioned it, I am guessing that Lary could afford any engine on the market. Lary and his sons have a very strong aviation background. When men of this experience and means study the options closely and select the Corvair, I take it as a compliment to our efforts. When we first started, the Corvair was seen as a low cost alternative for people economically excluded from hand-me-down certified engines. After two decades of development, testing, flying and teaching, the Corvair has now evolved to a top tier engine, a first choice powerplant.
Above: The engine during its first break in run. We operate it between 1,800 and 2,200 rpm for 30 minutes. The primary purpose is to break in the cam and lifters. We only use Shell Rotella 15W-40 oil for this, and we use an additive called ZDDP. We do the break in with slightly conservative timing, and run the engine on 93 unleaded fuel to avoid having lead deposits in the engine if it is going to be stored for a while before it is flown. In the presence of moisture, the byproducts of combustion from 100LL fuel can be corrosive over time. You can see that the run stand is chained down to an 800 pound concrete block we cast into the lawn next to the ramp. The only thing visible on the block is a 1/2″-20 threaded bolt hole. It is actually the balancer end of a scrap Corvair crank that we cast into the block. It’s not likely to be uprooted any time soon.
Above is a look inside the 3,000cc Engine. It is a big brother to the 2,850. The centerpiece of both of these engines is a drop forged, CNC machined, made in America, very high quality piston manufactured to our specifications. It has a very specifically designed pocket, and a flat quench area, for use with the 110 and 95 Corvair cylinder heads. The step that the head gasket sits on can be entirely machined out of the head so that the quench height of the engine is solely the head gasket thickness. This could be done before, but would result in an alarmingly high compression ratio. The pocket in the piston takes care of this, keeping the compression ratio reasonable. Other pistons for Corvairs have had little dishes cut in them before. But we had these pistons specifically forged with thick domes to allow the pocket to be machined as deep as it needed to be without compromising the strength of the piston. In operation, this engine has extremely high turbulence and very good atomization of the fuel, yet a static compression ratio that will easily run on 93 octane fuel without retarded timing. These combustion and ignition characteristics have the potential to make this engine more powerful than a 3,100cc Corvair with its required retarded ignition timing. There’s a number of other reasons we selected 3 Liters as our new standard large displacement engine, but the primary goal was to produce an uncompromised large displacement Corvair that will operate in a future where the affordability of 100 low lead may come into question. The 2,850 has the same characteristics, but it is the largest displacement that can be made without machining the case.
Above:The 3,000cc engine makes 120 continuous HP at 3,150 rpm. The engine has no difficulty making this power output and remaining cool while doing it. In this photo, the engine is running on the same MA3-SPA carb that we test all of our engines on. This is the most popular carb for CH-750s. Next, we will test this engine with a Precision mechanical fuel injector. It is expensive, but it is made by the same people who produce injectors for certified aircraft. We run the engines with cast iron manifolds and small mufflers to get it quiet so we can listen to the engine internally during the break in. This engine performed flawlessly. Grace’s 1946 Taylorcraft sits on the lawn behind the engine.
The engine above is built with a Modex-prepped forged and nitrided crankshaft. It has a Weseman 5th bearing, as well as a brand new valve train including the cam drive gears, lifters and pushrods. The forged pistons and cylinders are new and the rods are Clark’s rebuilt with ARP rod bolts. The heads have new seats and guides and stainless valves set with exhaust rotators and new springs. The engine has one of our new high volume oil pumps and a Dale harmonic balancer. It features all of our Gold Oil System parts,including the Billet Pan and Deep Sump Pickup, our Short Gold Hub and Front Starter System, a 20 amp charging system and our redundant Electronic and Point (E/P) Ignition System with spiral wound ignition wires. Because it varies from airframe to airframe, the carburetor is sold separately. We build these engines for $11,500. A dedicated builder working in his shop can build a clone of this engine for $7,500 in parts and about 150 hours of his time. (Smaller displacement engines like the 110hp 2,850cc and the 100 hp 2,700cc can be built on significantly tighter budgets.) We are glad to work with both groups of people. With other engines, the engine is always configured in the way that is easiest for the factory to make, or the most profitable set up. Your Corvair engine can be built in any way that suits your airframe, budget, timeline or personal goals.
Our main focus is, and will always remain, teaching builders how to build their own engines. This is the approach of 95% of the people we are working with. We are the only engine company on the market dedicated to giving people who wish to build it themselves access to a top-level engine. We build a small number of engines a year. These are done as educational showpieces that effectively demonstrate the potential of the engine. With this purpose, the engines we build are assembled out of the finest materials and parts. I personally assemble each of them, and I take as many hours as needed to do so. Afterward, each of them are given a long break-in run process, and then a final tuning. These engines only serve their purpose if they provide long trouble-free service to their owners, in the process demonstrating to observers how well the Corvair works. Again, 95% of these observers will choose to build their own engine with our parts and assistance. In plain terms, this means that our motivation when building an engine for a family like the Hatfields is to produce the finest engine, not the most profitable one.
Contrast this with traditional automotive conversion engines. Those engines were sold as the sole profit-maker by companies whose overriding goal was to make money. Many of these engines were based on things pulled directly from cars, cleaned and declared airworthy. Companies that did rebuild engines were tempted to cut every corner inside, because that’s how they were going to make more money. Most of these companies were LLCs with 3 year life spans. They knew that if they sold 100 engines in the 36 months, 90 of the engines would not be mounted on an airframe. Their high time customer engine would likely get less than 100 hours. If that guy had issues, they could keep him quiet by sending him an “updated” engine or offering him some money back. By the time the majority of buyers discover that there are issues, the LLC has folded up the tent, and they don’t have to stand behind anything. This isn’t a bad dream, nor is it far-fetched. When I got started in 1989, there were 40 or 45 nationally known alternative engine companies. Today, just 3 of these remain, and the only other one that still goes to Sun ‘N Fun and Oshkosh is Steve Bennett at Great Plains VWs. There were 15 companies offering EA-81 Subarus, all gone now. Zoche Diesel never turned out a product. The Cam 100 Honda, and almost all the other Honda people, are gone. A half dozen outfits that offered small turbines and delivered nothing are gone. So are most of the V-6 people, and all the V-8 outfits I can think of except one. These companies were designed and run to make money, not to last. When they disappeared, they took a lot of people’s money and dreams with them.
Corvairs have seen their share of these people. In the past 5 years their have been four LLCs that sprang up to make Corvair parts. All four are bankrupt today. All of them were previously customers of ours. Naming them doesn’t matter as much as understanding that there will certainly be new ones over time. While I feel some sympathy for people who were taken by these LLCs, it isn’t my obligation to help out the people stuck with orphan products, and this includes not having them at our Colleges. Everyone understands that your local Ford dealership isn’t going to work on a 1986 Yugo. It’s the same thing here. I include this as a reminder to builders that most of the people who start an aircraft project don’t finish it. Our builder completion rate is about 35% after four years. This is twice the industry average. There are a lot of reasons why the industry is so low. They are incentivized to sell you things, not teach you things. The journalists writing about planes generally haven’t completed a plane, and 95% of them have never gotten their hands dirty on an aircraft engine. There are countless Web sites with disinformation provided by people you will never meet. Reading them allows these people to affect your perspective and reduces the probability of your success. These factors are never going to get better, and in all likelihood are going to get worse. The good news is that you can exercise good decision making skills, pick the right people to listen to and learn from, work with proven companies and navigate your way through. Last year, nearly 1,000 new amateur built aircraft were completed and registered with the FAA. If your personal goal is to learn, build and fly, we will be glad to work with you to get your name on the next list.
Spark Plug Installation
Here are a few quick notes on spark plugs. Print this off and keep it in your maintenance notes. I have a 3 ring binder that I keep in the top of my engine building tool box. In it I keep any data that I am not going to memorize. In my case, this is part numbers for things that we repeatedly order by phone, CC vs. compression ratio data, and research notes and test data. Lots of stuff, like this plug data, I obviously have memorized, but the point is that well organized builders have notebooks and reference data, and it is a good habit to develop, especially if your workshop and home are not at the same place.
What plugs should I use? A common question. At our place, I often use Autolite 275s just to run engines on the ground. People have flown them, but the primary use I put them to is break in runs. They are in stock at most chain auto parts stores, and are often on sale for less than $1.50 each. I still like AC R44Fs for everyday flying. People have flown a giant variety of plugs, and the engine is not that sensitive to them with one exception: Do Not Fly an engine that will use 100LL fuel on platinum plugs. Other than this, make sure the plug you are looking at is the correct application. For many years the Bosch catalog listed for the Corvair a plug that was 3/16″ too long, and actually hit the piston head. If you are thinking of trying a different plug, go with one that people have already flown in a Corvair like yours, with the same carb and the same kind of fuel. For example, Woody Harris has a lot of flight time in his 2,700cc and later 2,850cc engines using Denso iridium plugs, part number IWF16-5359. His plane has an MA3-SPA carb and flies on 100LL. If you want to eliminate variables, use R44Fs, as they have proven to work well on the broadest variety of engine configurations.
How much torque do I put the plugs down to? This is a very important question. People used to cars with iron heads always overtorque Corvair plugs. The Corvair Shop Manual says you can use 20 pounds, and I have had new builders ask if 25 or 30 was ok, as they didn’t want them to “get loose.” If you routinely torque them that much on installation, they will get loose, because they are going to strip out of the heads. A much better number to work with is 7 to 10 pounds. I use 7 pounds more often than 10. After an initial ground run, I will recheck the torque. The Corvair’s plugs seal by a gasket, and it takes almost no pressure on this to get it to seal. Don’t overdo it; it isn’t a lug nut on a diesel truck.
Above, final prep work on Lary Hatfield’s 3,000cc engine destined for service in his Zenith 750. I built the engine for him in our shop this week. It has all our Gold Systems and one of the Weseman’s Billet 5th bearings. After careful set up, the engine fired up after 3 seconds of cranking and laid down a flawless and smooth 1 hour break in run. Notice how short my personal plug wrench is. It is a 13/16″ plug socket with a hex top. I apply the torque with a cut down 12 point offset wrench that is only 4″ long. This arrangement fits in a small storage space. Because the wrench fits on up or down, it is very easy to use in confined spaces like the front two plugs without the Nosebowl removed. The bottle on the head is Champion plug lube.
What should I use for anti-seize? There is only one substance you should ever put on any plug in an aircraft: Champion 2612. This is the only stuff that aircraft mechanics use. It is black graphite liquid with a tiny brush. It does a neat, controlled job. Over the years, I have seen a great number of planes of all types with plugs coated in silver anti-seize. I have seen people apply it in the thickness one might better use to put peanut butter on a sandwich. Its brush is sized to apply it to diesel truck lug nuts, and the stuff is messy, and conductive. I have seen builders get enough on their fingers and on the ceramic part of the plug to cause a short, and make the plug boot slip off the plug. Stay away from it, get the real stuff. Aircraft Spruce sells small bottles that go so far that I am only on my second bottle in two decades of being an A&P. They cost less than $10.
What gap should I use? The ignition systems that I build are not too picky about it, but start with .035″. Measure it with a wire, and use an actual electrode tool to open the gap if required. Resist the temptation to pry the gap open with a screwdriver or a feeler gauge. As always, if you have any questions, give a call or write in.
Fuel Injected Corvairs
Note to readers coming from the Cub Crafters site: This information is not directly applicable to Lycomings. The 6% power increase came from a major change in the intake configuration, not from the EFI. Look at 360 Lycomings; Yes most of the ones with a carb are 180HP and most of the injection are 200HP, a 10% gain, but this is ignoring the fact that the 200HP models (the -As and -Cs) have a very different angle valve head and a tuned induction system. Note that the 360s that just change from a carb to injection, (the -B series) remain at 180hp. There is no magic power in FI. Also note that all Corvairs in the last decade all have electronic ignition. If a Lycoming has a perfect set of mags and they are replaced with electronic ignition, there is no reason to expect a measurable peak power increase. The far easier way to get a small power increasein almost any motor without adding any complexity is to turn it slightly faster. -ww.
Here are some notes and photos of five fuel injection systems for the Corvair. The first three are electronic systems, the latter two are mechanical injection. Fuel injection is a topic that many builders ask about. I think a lot of the interest is generated by the awareness that high performance certified aircraft have mechanical fuel injection. A number of builders have learned that these systems are comparatively immune to carb ice. Beyond this, very few people have a good concept of the pros and cons of these systems vs. carbs. Even guys who know a fair amount about engines often miss important realities about the applications of these systems. This post gives a general overview, and covers details that are rarely discussed when builders bring up the topic of injection.
Electronic injection is the type of system that modern cars use. There have been a number of auto engine conversions that came from cars that had EFI that have gone on to fly in planes, and some suppliers to certified engines are just starting to look at EFIs fitted to Lycomings. What gives modern cars good mileage, long plug life, low emissions, etc., is the ability of the EFI system to operate in closed loop mode. It does this almost all the time the car is cruising down the road. When it is not doing this, it is operating in “open loop mode” and falling back on the computer’s pre-programmed data that says ‘at 3150 rpm and 26.5″ MAP squirt in so much fuel.’ In open loop, much of the advantage of EFI disappears. Up to here, what I have typed falls into the category of “Lots of people know this.” Here is the corollary only a few people understand.
In aircraft applications, the EFI systems almost never operate in closed loop. If you are going to cruise your aircraft at 75% power, it will spend its whole time in open loop. This is true with liquid cooled engines, but really true with air cooled ones. Very few engines run with air fuel ratios of 14.7 to 1 at high power settings. They mostly run 12 to 1, or richer, and O2 sensors have a hard time getting the loop to close at rich ratios. Sure, there are exceptions to this, like wide band sensors, but you really cannot compare a made at home system to a 2007 Corvette with perfectly tuned knock sensors, 1 million lines of code in memory, and the ability to look at individual cylinder exhaust pulses as they pass the O2 sensor. Even still, GM knew that 75% sustained power in the Vette would be about 155mph, and the car would spend .002 percent of its life there, so it’s OK if it is in open loop at that point.
After CC #9, I got Mark from Falcon to walk over to Jann Eggenfelner’s hangar. Jann is the king of Subarus, and like it or not, most people concede that he has flown more different types of EFI than anyone else. I know him fairly well, and he is very smart, and unbelievably tenacious. With Mark’s OEM background and Jann’s flight experience, they had a very detailed high speed data exchange. The recurring point that Jann kept coming back to is that no system, including the Subaru OEM stuff, will reliably operate in closed loop at aircraft power settings. In open loop, EFI begins to look like a very complex, high pressure, electrically dependent carburetor.
Above, the EFI 2,700cc Corvair built by Mark at FalconMachine.net in 2007, at power on my dyno. The urethane wheel directly reads foot pounds of torque off the digital scale. Note that this engine is using headers with collectors. We also tested it with cast iron manifolds and mufflers. It has distributorless ignition. Six LS1 coils are mounted on the sides of the black airbox. After a lot of careful calibration runs, this engine achieved a 6 percent power increase over a carbureted Corvair. Merely saying this will certainly activate the keyboards of armchair EFI experts, but it’s simple measured facts. Before questioning the test methodology or results, consider that Mark has earned his living with these systems for the past 20 years and the instrumentation included such niceties as a $500 laboratory grade digital oxygen sensor. Anyone who says that adding EFI to an engine like a Corvair will add 30% more power is just making their information up. The system above was tested a number of hours but was not flown. The controller on this was a Tracy Crook unit. This engine was equipped with equal length intake runners. It was laid out to fit in a 601/650 cowl.
This is a redundant ignition, electronically fuel injected, fifth bearing, 2,700cc test engine built by Roy at RoysGarage.com in 2007. It features coil on plug technology and throttle body injectors along with a rear mounted 40A alternator. It is mounted on Roy’s 701. It was run and tested, but not flown. Roy also has extensive experience with digital EFI systems. This provided good data, but in the end, Roy thought about the complexity he was applying to a very simple aircraft and chose to finish the aircraft with a simple gravity feed carb instead.
My thesis on EFI in 5 simple points:
1) 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. EFI runs at high pressure.
2) 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, like digital EFI.
3) Any system that has less parts and connections is less likely to fail. Digital electronic connections, working at low voltages, are very sensitive to corrosion, temperature and vibration, things planes produce more than newer cars.
4) Almost all the things that EFI advocates hope for, HP increase, smoothness, fuel efficiency, and reliability, will prove elusive or minimal. Before debating this, seek out a single flying system that will go into a closed loop in cruise flight. Realize that monitoring voltage and fuel pressure is not a work load reduction from using carb heat.
5) 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. This is a valid position, and I support anyone who knowingly makes it.
Let me introduce a man who personifies point number 5, Rex Johnston. As far as I know, Rex is the first guy to ever fly an EFI system on a Corvair powered aircraft. This makes him someone special, because there were a lot of hurdles to jump over. His Corvair powered plane is a Davis DA-2, a sporty little two-seat sheet metal aircraft. Rex’s work is an outstanding example of building to meet a challenge that you personally feel. He was not after some illusive performance goal, he was just looking to challenge himself and learn a lot. Hats off to Rex.
Above, the underside of Rex’s plane. His system is a Holley Projection throttle body unit, that Holley originally sold for 258cid Jeeps. Rex’s engine is a 3,100cc Corvair. Notice that it still has carb heat. A project like this isn’t for everyone. It takes significant experience building to be able to develop and flight test a complex set of systems like this.
The standard for aircraft injection are mechanical systems. These use no computers, they work entirely on a balance of pressures and flows. They meter fuel very accurately, and offer instant throttle response. They typically operate at 25 psi, somewhat lower than EFI. Unlike EFI, they are not sensitive to fuel pressure changes, and they do not need an external pressure regulator. By design, they are always operating in open loop mode. Because these systems have been used on aircraft for half of the history of powered flight, they are fully understood and developed.
The above photo shows an Airflow Performance mechanical fuel injector specifically calibrated for the Corvair. For size reference, a core Stromberg carb is at top left in the photo. Below it is the gold flow divider. One of the installation advantages of mechanical injection is the extremely small calibrated nozzles. Packaging six electronic injectors that will fit in a tight cowl is challenging. Mechanical injectors have an 1/8″ pipe thread on the bottom and are roughly 1/4 the size of electronic injectors. Airflow performance is owned by Don Rivera, a very smart guy who has owned and driven land-based Corvairs. This system is made in the U.S. The parts for this system cost over $3000. Corvair builder Sarah Ashmore is putting one of these on her Personal Cruiser airframe. Her heads were modified for the injectors by Mark at Falcon. She works in the aerospace industry and made the choice to equip her aircraft with a system that met her specific goals.
Above is a photo of a Precision mechanical fuel injector. The pictured unit is a port injector, but they also make a very compact unit that has the same quality, but has just one injector built into the body of the unit. The system does not require any modifications to the Corvair’s heads or intake, as the unit bolts onto the same flange as an aircraft carb. Peter Nielson of precisionairmotive.com is our engineering rep who has supplied us with a test unit, which we are now testing on a 3,000cc Corvair. This system is about $2,500. Precision knows quality, as they produce parts for and service certified fuel systems. We will release more data as we move through the tests. We are planning on flight testing this on Woody Harris’ 601, and Dan Weseman is planning on using the aerobatic capability of the system on the prototype of his new Corvair powered design, the Panther.
Today, 99.75% of Corvair powered planes use carbs. However, I think the Corvair is a good platform for fuel injection, and there are a small number of airframe applications that could really benefit from a fuel injection system. While there has always been a lot of talk about EFI, only a rare few clever and persistent builders like Rex Johnston will see the project through. I personally feel that the mechanical systems offer the best reliability and most proven track record, having flown in many demanding settings on other engines. As always, the proof and the progress is in the hands of the builders, the people In The Arena.
The subject here is the most popular light aircraft carb of all time,the Stromberg NAS-3 and 3A. These were fitted to roughly 70,000 aircraft over a production run that lasted several decades. It looks like a very simple carb, and in some ways it is. But in reality, it is a highly engineered design that was produced by the world’s leading manufacturer of aircraft fuel systems. At the time of production, this was Stromberg’s most basic product. They also made ultra sophisticated pressure carbs that were on the most powerful multi-row radials. This carb comes with an experience pedigree that no experimental carb can come close to matching.
Above, a Stromberg NAS-3 mounted on Dave the Bear’s Wagabond. We finished this aircraft in our Edgewater hangar in 2004, when Dave worked as part of “The Hangar Gang.” We used this combination with a 2,700cc Corvair and a Sensenich 64×35 prop to conduct a lot of jetting tests. We were not new to the Stromberg, as our Pietenpol, and our second test mule, Gary’s Skycoupe, both used the same carb. Besides these Corvair powered planes, the carb was also on several certified planes we had at the same time like Grace’s Taylorcraft and Gus’ 120.
When it comes to gravity feed carbs, I like Strombergs because they have literally millions of hours feeding air and fuel into flight engines. I know them and trust them, and if I had any little issue with it, I’d have a mountain of expertise to draw on, not just other people flying one, but professionals with decades of documentation. I don’t have to think about it, it isn’t a variable. The one limitation on the carb is that it is not suited to use on a plane that requires a fuel pump. Thus, it isn’t good for a 601XL or a 650, but it is a good match for any high wing plane or one with a header tank. (The sole exception to this is the 750 because the factory now recommends that builders use a back-up fuel pump because of the plane’s high angle of attack capability.) I consider the Stromberg a much better carb for the Corvair than any of the other gravity feed carbs like a Monett Aerocarb, Posa, etc. The typical price for an old but functioning NAS-3 is $250. If you shop around, you can find them for half of this.