I just purchased a used Rossi 40 from a guy here on rcu. It is an older engine, probably late 80's model, but it is in good shape and has good compression. I ran the engine yesterday on a cougar and could only get around 12k out of it. I'm turning a 10-7 apc and running cool power 5%. Shouldn't I be getting a lot more rpm out of this engine? The overall performance of the engine and throttle response is good. I just figured it should run up a little higher than what I'm getting. I was told by someone here on rcu that this engine should only be run on 5% nitro but a guy I fly with said that over the years he has had many high performance engines and he has run higher nitro in them with no trouble. Could this engine possibly run better on higher nitro without having to shim the head? I'd like to be able to get a little more out of this engine if possible.