We are often asked about using non-aircraft engine conversions. We’d like to pass along a quote from a colleague in the homebuilt airplane business:
 "the best conversion I know is to take $8000 and convert it into a good used Lycoming." This may sound a bit narrow-minded, but it reflects the basic truth: no non-aircraft engine has yet proven to be as reliable, available, and inexpensive (everything considered) as a traditional aircraft engine.

It seems that magazines are always printing stories about automobile engines bought for junkyard prices, mated to inexpensive reduction drives and flown off into the sunset. It simply doesn’t work like that in the real world. The reliability we have come to expect from aircraft engines is the result of years of development and refinement of engines designed specifically for the task. Automobile engines function well in their intended application: delivering low cruising power in vehicles with well designed transmissions and power trains. Using them successfully in an airplane requires continuous high power outputs and reduction systems coupled to the propeller. This is completely foreign to their design intent. (You can imagine the car engine designer banging his head slowly against his desk..."no, no, no. If I’d known you wanted to do that with it, I would have designed something different....)

With enough research and development effort, auto engines may be made to work acceptably or even well in an airplane. We are not opposed, in principle, to RV builders using alternate engines, but we would hope that this choice is made on facts, not hopes or dreams. Do you want to spend your time and effort on engine development or do you want to fly confidently behind an engine that has already been developed?

We, too, would like to see "something better" in available powerplants. We are carefully watching some alternatives. Meanwhile, the proven Lycomings do the job very well and are the best "available now" option. Despite the many claims and promises made by promoters, we feel that if you will look closely at what is actually available, how many are really flying, and how well they really perform, you will agree with our conclusions.

While we are not opposed  to RV builders installing alternate engines, we simply cannot recommend or encourage the installation of any other engine - we don’t feel it would best serve the interest or safety of the builder.