Of the three popular Corvair displacement that we promote, the 2700, 2850 and 3,000cc engines, only the last one requires any modification to the Corvairs case. To build a 3,000cc engine, both the heads and the case need to be machined where the new 3,000cc cylinders are bolted on. Again the 2700 and 2850 require no modifications to the heads or case.
Several years ago, Dan, Mark Petz, Roy and myself, got together and came up with an exact set of specifications for the 3,000cc machining, to ensure that any builder could be assured that parts sourced from any of us would be compatible. Previously there had been a number of suppliers for 3,100cc parts, and each of them had their own way of machining, and builders were often stuck with one of a kind engines, or even engines that had to have individually machined cylinders for each hole. When developing the 3,000cc engine the four of us were determined to eliminate this issue.
The single biggest factor aiding the standardization of the 3,000 over the 3,100 is the fact that the design and geometry of the 3,000 is all Corvair, compared to the 3,100 which has the piston pin and compression height of a VW engine. These compromises make the 3,100 require modified rods and custom length pushrods. The 3,000cc engine, by our design, uses stock Corvair rods and standard length pushrods.
There are a number of other advantages to the 3,000 over previous large displacement engines, but I would like to steer back to just the machine work required for this discussion. (A 3,100 engine also required the heads and case to be machined to fit the larger cylinders.) The primary reason why we went to 92mm as the 3,000cc bore over the 3,100s 94mm bore is to improve the head gasket area and decrease the oversize required when machining the case. A 3,000cc engine’s case has the 2mm difference in case bore, this may not sound like a lot, the it is a great improvement if you need to put a helicoil or timesert in the case for a head stud. On the top, the 3,000cc’s head gasket does not break out into the head stud holes as the 3,100 does.
The above photo is from our website in 2008. It shows a highly modified 140hp cylinder head that flew 200+ hours on our 601. The head gasket area extending to the head bolt holes shows it to be a 3,100cc head. (look at the bolt hole all the way on the right side of the photo.) It has flanged VW exhaust, a modification that I no longer think is a good idea on any flight engine. This head has since flown 400 more hours on Dr. Andy Elliott’s high performance 601 XL taildragger. A strong word of CAUTION: No one should consider using stock 140 heads on any flight engine. They are notorious valve seat-droppers, and will actually produce less horsepower on typical 2,700cc engines. Flow-wise, they only make sense on high rpm 3,000’s and 3,100s.The 3,000cc engine we are building for our own aircraft has a set of Falcon heads from a 95hp Corvair. Over the years we have tested countless ideas and concepts. Some, like the heads above have limited application in the hands of the right pilot. The amount of time I spend working directly with builders gives me a very good take on what they are personally looking for in an engine. Our testing allows us to suggest which Corvair will provide what they seek.
If you are heading to College #23, and you are thinking of building a 3,000cc engine, you need to send your case in for machining to Dan very shortly. Several cases have already arrived, and Dan is setting up his very accurate tool room mill to machine these cases. The cost of this modification is $150. Dan wanted me to point out that it isn’t practical for builder to bring their cases to the college and have Dan try to machine them the same weekend. If you are planning on a 3,000cc engine, this is the week to scrub the cases, pack them carefully, and send them to Dan. We will have them ready for assembly at the College. (If your building a 3,000, but can’t make the event, you can still send the cases in for the machine work.) Again, this work is completely compatible with the 3,000cc kits sold by Mark Petz at Falcon and the kits sold by Roy.-ww