Hi guys, this is my first visit and a therr is 190 threads on engines and no search window I'll start another question.... Has anyone used a motorcycle engine such as a Suzuki GSX1100 CC on a 2 place gyro? Cheers Doug.
I have nothing specific to report about Suzis. Any time you propose putting a surface-vehicle engine in an aircraft, though, remember the "duty cycle" issue. Surface vehicles don't use that much power at cruise (especially motorcycles) . They use full power typically for only seconds at a time. Their designers therefore design for this type of duty.
An aircraft engine OTOH must be capable of continuous 75% or so output without overheating, breaking, blowing up or wearing out after 50 hours. It also must be able to run full-throttle for at least 5-10 minutes at a time, and preferably for an unlimited time (to permit long climbouts). Surface-vehicle engines very frequently can't take this kind of treatment for long. If their designers DID design them to take it, they'd be fired for wasteful overdesign.
The answer to reliability for a surface-vehicle engine in an aircraft is often to de-rate them. Suddenly your 200-horse engine becomes a 125-horse engine, and the power-to-weight ratio looks less appealing.
Surface-vehicle engines often make their power at high RPMs. A propeller can't use high RPMs, so a reduction drive must be added. The bending loads and torsional feedback from a prop are pure torture on a re-drive and/or the engine crankshaft. Both adequate bearing support and some softness/slip must be built into the drive.
It can be done, and has been, but it's not a trivial project.
Doug, I think that because most motorcycle engines have the transmission as an integral part of the crankcase, people have stayed away from them (how do you get rid of that extra unneeded weight?). However there are several examples of Yamaha snowmobile engines (which do not have the integral transmission) that are very similar to a GSX1100 type engine.
Thanks for your input fellas, on further investigation I've decided to go the reasonably tried and tested path of the JE 22 Subaru motor at 130HP with a bulletproof alloy block which has 280Hp from a snail in the JE25T donk extracted successfully from it. Thanks again, Doug.