Deanoo, Spacey is correct. The 32SX-H is the heli engine, the 32SX is the aircraft version. It has the same mounting pattern and dimensions as the 25 fx (for the most part) but a lot more power. I am running a 10X6 airscrew at nearly 13,000 RPM on a 4lb. TT Lazy Tiger 51. It will hang on the prop.