I am flying this plane with a O.S. .40 FP just because that is the engine that I had. If I were to buy an engine just for this plane I would buy an O.S. 46FX with a Slimline Pitts muffler.

I have heard of others using larger engines but I think the .46 will give you plenty of power.

BTW: This is a really fun plane!! Snap rolls are incredible!