From what I've heard others say, the .46 would be good, but would give you no excess in power. A .40 would be too small. This plane is not very heavy, so it doesn't need a lot of power. However, I'm planning on putting a saito 100 in mine, which is very much overkill. There's been some discussion about that, which you can go back and read. I'll let you all know next week how it flies with a 100 turning a 14 x 8 prop!