I think I'll stick with Hot Mod or EB Mod. In a hobby where precision is neccesary, the engine is the last thing I'd want to mess up with by hand. I have owned a Hot Mod S421BNX and it was by far the best engine I ever had. It lasted 9 gallons. It had so much bottom end power while having tons of leg on the top end.The best thing about it was the fact that the power ratio was very linear and smooth. Even my JP B5 was brutal on the bottom comapred to it. For now I have a Max Power MX21 M5B to play with for next season.