It all really comes down to the physical size comparison (will it fit), weight comparison (watch wing loading), and power comparison (ability to turn a given prop at a given rpm). Aside from that, different makes and models of two or four stroke glow, or gas engines all of the same displacement can vary greatly in power. You can compare cubic inches, or cubic centimeters for a displacement comparison, but the power/weight/size comparison will be quite different, and in the end, what you are really concerned about.

Chad