Engine Displacements

From Jerry Tolman:

This blog is a great start to 2012. Thanks. I have a suggestion for a discussion…post a brief summary of the differences in displacement choices for those of us still early in the engine build or still deciding?
And a question…planning a West Coast Corvair College this year?


Good to hear from you. First, we are thinking of holding an event in California this year. We are looking at May 5th weekend in Chino at Steve Glover’s hangar where he runs NVaero. Steve is having a KR gathering there and an open house at his shop that weekend.  I have known Steve for many years, and his two commercial hangars at Chino are well equipped to have a very productive College.  Steve and I think that having the two events on the same weekend would be a good exchange of people and ideas. The Corvair is a very popular engine choice in the KR, and Steve wanted all Corvair builders to understand that they are more than welcome at his place. (Besides owning a series of KRs, Steve also has a Long EZ and a TriPacer; he is an all around aviation guy.) The only thing that has kept me from putting it on the schedule is a 50/50 chance that the weekend will conflict with my brother-in-law’s retirement from 30 years in the Army. In our family, such an event is “AHOD” (all hands on deck). We will know more in two weeks, and post the information here, under the “Events” heading.

On the subject of engine displacements: Today I encourage people to build one of three engine displacements that makes sense to them. Here is a breakdown:


2,700cc, 100hp, based on stock Corvair cylinders which are rebored from .020″ to .060″. Requires no machining to case or heads.  Uses either Sealed Power or Clark’s Forged pistons. This is the engine that 85% of builders are working on. More than enough power for a Pietenpol or a KR, a good choice for a 601 or 650. There are many flying examples of each of these airframes with this engine displacement that have individually logged hundreds of hours each.

2,850cc, 110hp, based on Clark’s heavy duty brand new full fin cylinders bored .105″. Requires no machining to the case or heads, it is a straight bolt-together engine. This engine uses U.S. made forged pistons that are available through us. We sell a Piston/Ring/Cylinder/Rod Kit for $1,750. The pistons have a 7.7cc dish in the head to lower the static compression while maintaining a very tight quench area, giving the combination of good combustion and outstanding detonation resistance, even on unleaded fuel. The engine is also the best choice for later turbo-charging. The displacement is a good choice for any Corvair powered airframe. Photos of CC #19 show Jeff Cochran’s running 2,850 built for his 750, and you can look at CC #21’s coverage for pictures of Clarence Dunkerley’s running 2,850 that he built for his Cleanex. Our Web site coverage of Oshkosh 2011 has a lot of photos of Woody Harris’ 601 that he flew on a circumnavigation of the U.S. Woody’s plane is powered by a 2,850.

3,000cc (3 liter) engine, 120hp. This is based on custom machined cylinder castings that are related to VW castings. The bore size is 92mm, but we use the HD casting that is the same as a 94mm VW cylinder. The piston in this engine is the big brother of the 2,850. It is forged in the same U.S. factory, and features a 10cc dish. This provides the same combustion characteristics in a slightly larger displacement.  This engine does require having the cases bored slightly for the larger cylinder spigots and having the head gasket area opened up slightly. This job must be done accurately, and the price is included in the Piston/Ring/Cylinder/Rod Kit. This displacement is a good choice for any Corvair powered aircraft. It has flown on both the 601 and 750.

Given these three engines, we no longer steer builders toward previous engines like the 3,100.  There is nothing wrong with 3,100s, but they did prove difficult to build for many people without a lot of previous experience. The internal dimensions were a compromise because the 3,100 used a modified VW piston with a different compression height, requiring the engine to be built with custom length pushrods, etc. The 3,000cc engine was our clean sheet of paper, based on what we knew after 10 years of building 3,100s. A 3,000cc engine is a better engine from a number of angles, and is a better engine choice for builders considering using unleaded fuel in the future. 

Thank You