My 4-40 was powered with an OS40 Surpass swinging an 11x6 Master Airscrew prop and it was a perfect fit for the design. I am sure that one of the hotter 25s would fly it. However, a mild 2 stroke 40 would also work just as well. I'm not sure that you would want to put in a fire breathing 46 in it. With the right power package, it is a delight to fly.