A trusted friend flew one with a 1.20. Said it was one sweet flying bird. He may be sort of an old school flyer, you know, no 3D, just smooth and graceful with the basic aerobatics. I guess I fly that way to some extent. So, his suggestion is that a 1.50 is good. Midwest recommends 1.50 - 2.7 four stroke. Great Planes Super Skybolt's recommended 4 stroke is .91 - 1.20 with only 3" less wingspan than the Stinker. However, before I buy the powerplant I'll do a little more research. There's always Saito's 1.80.