Intakes and Internet myths


Everyone who reads my notes regularly knows that I bitch and complain about how well the internet serves as a venue for anonymous “experts” to pretend they are smarter than people who are actually out building and flying. Maybe it’s been a few days since I shared another example? Heres one that was served to me on a silver platter. It also involves a common myth about engines that is a favorite topic of arm-chair engineers and experts.

Above is a picture of the 3,000cc Corvair we assembled for the Panther prototype just before Oshkosh. The Corvair all-stars shared a display at Oshkosh again this year, and the Panther with this engine on it was the centerpiece of the booth.  This angle shows how GM engineered the intake logs with an offset in them, this is specifically related to the flow vs firing order. These heads have astoundingly good mixture distribution for a carborated  engine. This has been confirmed by a number of flyers with 6 cht’s and 6 egt’s. On his own website, a very nice guy named  Steve took the time to say that he went to Oshkosh, met Dan and myself, that he really liked the Panther, and he put up a number of good photos that he took himself of the airframe and engine.

Enter the Internet expert…..Identified only as”Toolbuilder,”  from California. Although this guy was not at Oshkosh and probably has never seen a Corvair in person, he posted the following comment on Steve’s website. 

” I’m not a fan of the intake and exhaust on that Corvair. I think there is a lot of power that was left on the table when they went with the log style manifolds. To me, that’s the last resort, and you only go that way when the proper individual runner manifolds won’t fit. I’d bet there is 15 – 20 HP hiding in that engine with proper manifolds.”

Where do you start with an anonymous ‘expert’ like “Toolbuilder”? Do you think his friends told him that the email name he selected is also a specific low ranking job on a pornographic movie set? Maybe they knew this when they suggested it to him? Should we talk about how many dyno runs of Corvair engines he has made to offer a HP improvement so specific? Maybe we should just confine it to a small historical comment and a photo of a Corvair on our dyno….

Allison V-1710

Above, an Allison V-1710 cid V-12 engine from WWII. This engine is a General Motors product, just like your Corvair, Not in today’s Corporate merger sense, but in a very real sense, when GM owned 100% of Allison and all of their engineering was in-house American designs. Like my previous post on Detroit Diesels, this give some perspective when I point out that for 40 years, GM was the worlds largest business, with more engineers and resources than any other company on the planet.

Look at the intake system: Note how it is broken into four groups of three cylinders, just as the Corvair is set up as two groups of three cylinders (each head).  Look at how the incoming pipe is offset on each one of these groups, just as it is on the Corvair. This is not a coincidence, it is engineering. The Allison was originally designed to work well as a naturally aspirated engine just like your Corvair, and this is the proven way to get good mixture distribution at the rpm range we are speaking of flying. Keep in mind that these engines, and radials and Merlins were all “wet flow” engines where air and fuel were flowing through the intake, Just as we set up Corvair flight engines. This is different that modern cars that are only passing air through the intake, waiting to the last moment to inject the fuel. Although many WWII engines were injected, it is done way upstream by the supercharger.

Allison V-1710-109 V 12 Cylinder Aircraft Engine 1

Above is another overhead view of an Allison engine. Look at the layout of the intake pipes in the Vee of the engine and see that they are grouped in four sets of three with the off set in the feed pipe to each group of three. I didn’t invent this, but I am smart enough to copy it, and I am certainly smart enough not to say I know how to make specific improvement on engines I have never seen. Barring that, I know how to avoid having an email name with double meaning.


Above is a good illustration of the Allison’s system. There is a giant myth that the Rolls Royce Merlin engine was a fantastic design and the Allison was a second-rate engine. This myth is held by people who love all things British.  (Yes I appreciate, MGAs, Triumphs, Rhona Mitra, and Led Zeppelin, But not as much as Corvettes, Buells, Raquel Welsh and Chuck Berry.) The Allison is an outstanding design. For Fans of P-51 Mustangs, go read up on F-82s and realize that the prototypes had Merlins, but the production planes, the ones that did 480 mph and shot down jets in Korea, had Allison engines.

Above, the EFI 2,700cc Corvair built by Mark at in 2007, at power on my dyno.  How do I know that header pipes and independent runners will not make the “15-20 hp” that “Toolmaker” claims? Because here is that test, actually done in reality, years ago, not on vapor ware or in the imagination of an internet personality.  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 Corvair running on a carb, it’s simple measured facts, but it also ignores the fact that such an exhaust fitted in a cowl will offer a lot of surface area for heat issues and weigh more, and it cost 2.5 times as much to build as a regular Corvair. (A plain old 2850 makes more power than this elaborate 2700. Displacement beats electronics and theory.) Because of the structural strength of the stock log was lost with the individual runners, this engine actually popped a head gasket on its first run. Mark later made thick reinforcement plates and welded them to the heads as stiffeners to do what the cast in log does.

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 having an intake or exhaust change will make 15 -20 more horse power is just making their information up.

The internet will serve up a continuous stream of such experts who think that they can look at a photo and instantly improve 20 years of testing and development by 15 -20%. I am sure if you asked this guy, he would also tell you he knows how to make a Van’s RV-4 go 300 mph and how to make your car get 100 mpg.  People like this have never done anything to share useful information that gets rank and file homebuilders into the air with proven information they can count on. -ww

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