Louis B's answer is perfect! But please pay more attention on your rotor pitch curve setting. Try to adjust your throt curve and rotor pitch curve make your engine and rotor goes faster. I hope it works.

And if you want to change a engine 40 and 50 both Ok, but this need a little bit ajustment on your heli to fix the engine. And I believe the 50 engine can use longer with a 30 body beacause it takes low pressure compared with the 32 engine.