It looks like Lycoming engines are by far and away the most popular for the LongEZ. It's really hard to find example of anything else except Lycoming. Mogas might have ethanol and I've read that the acholol will eat away at the original plans fuel tanks. I think the engine accessory systems are also harder to custom install on other engines. The original plans, I believe, warned against the Continental O-200 because of great difficulties getting it all hooked up. (I wonder if that ever changed) Still, I haven't heard of a single person with a LongEZ O-200 (probably the low HP output too). I wonder matching prop to engines is a big difficulty to get it right for the LongEZ. I've read that the prop needs to be long because of turbulence hitting the center of the prop, causing it to "swat" at the air. But farther out from the prop (with a long prop) then the airflow is smooth, and the problem is gone. With Rotax engines, they have a gear-box drive system because the RPM is so high, to otherwise slow the prop down. It has a clutch in the gear-box that "protects the prop" from prop strikes. That sounds like a good thing with the LongEZ, but maybe the prop "swatting" at the air in the center burns the gearbox clutch up? (Do the wheel pants help? I've read they slow the plane down. Are there alternatives to protect the prop without all the glory of wheel pants?) I'm not a mechanic, so i might be using poor terminology there. One other thing, of course I've been googling Horsepower and engine prices and fuel economy and figuring out which engine does what, but I've noticed HUGE differences in engine prices, even for the same model. I know some are rebuilt, and others are brand new, but still I see enormous price differences googling aircraft engines between 100 and 200 horsepower, even for the same model. I wonder if some of the prices are "installed by a mechanic" and others are "here you go, put it in yourself" varieties? Those are just a few more thoughts I had on engines on LongEZ. If anyone has any thoughts about this for the LongEZ or the VarieEZ, please comment. Thanks.