they make a 32 and 36 on a smaller case. One of our guys has the 32. It was a super engine from the first flip. Always easy starting, plenty of power, at least on a speed limit combat plane. The 36 would be a better bet for stunt, although the 32 runs fine. Check the weight on the 40 before you get one. If it is a 40 built on a 46 case it will be heavier than need be. The smaller engines are built more along the lines of a 25 sized case.