Thanks for the input guys. I was wondering about a 13x4. I put the 14x4 on it and it would not tach over 8500. I took it off immediately. I also noticed air bubbles in my fuel line. turns out I had to remove the tank and redo some foam. It flew alot better. I also put the 13x6 back on it. It would tach around 9700 but I think I got it a bit lean. OOPS!!!! It would climb alot better after the fuel tank fix, but still would not hang on the prop. I guess if it wont hang on the prop, I will just enjoy it until I get my bipe and over power the he!! out of it.