Hi, I have a similar question.
I'm using a cheap 8 port .21 for practice (sh engines pt21xt2-p8). Actually the performance of this engine is not so bad but I would like to bring it closer to my race engine and am thinking of trying a higher nitro percentage fuel, maybe 28 or 30%. Runtime is no issue as just for practice but will wear be much higher? Should I shim the head up? Change plug?
Will it actually have much more power, and where in the power band?

Thanks.