When did AP copy Norvels design? Ah man, if I had it on me I'd do it. BUT then what would I do with the ones I'm not using in the basement? Lucky, if they did a direct copy or just got the rights from Norvel and they are the same tolerance these will fun fine on 5-10% nitro fuel. The Norvels ran great and we're very durable. Never got that muffler to work well. Spring loading tends to just vibrate around and rub metal to metal, not a good thing in model engines. Make sure and use Hi Temp RTV on clean surfaces to seal that gap. We just ran them straight out. I don't THINK I had them on my 1/2A racer. Definitely not on my CL planes.