Forgot to mention, those engine sizes are for four stroke engines. I wouldn't put a 2-stroke engine in a Cub. I have friend who has a WM .40 with a 46ax in it and I can't say that I recommend that combination to anyone. Yes it flies well... but it does so like a scalded cat! For cruising, nothing beats the low down torque and thumping bass of a four stroke engine. Many would argue that gas engines sound better. Personally, I can't say I love the sharp barking sounds of gas engines. But to each his own.