OS does state that the LA series can run on fuel with 5% ~ 15% nitromethane. Following this information that OS has provided, it would seem 15% is the limit. Don't get me wrong, I'm not knocking anyone that chooses to use 15% in a bushed engine, but that engine should run just fine on 10%. More nitro = more heat. More heat = more friction. More friction on the bushings = more wear. OS doesn't care, they'll gladly sell you a new engine.