Propworn I will say you are wrong when it comes to YS engines and you don't know what you're talking about. 75% nitro is not recommended and only a few have run that much. Some in the past have run 65% in the 91 and 120 engines. You say you have seen as high as 40% nitro used in a YS yet claim anything above that is useless lol take two airplanes same weight, same design and both with the same YS engines and the one running 60% will be faster than the one with 40%.
Know this I race these engines ........ so I have experience and knowledge on them
You have seen up to 40% this could mean you have seen other people run that high and not your self so either way your knowledge stops at 40%
YS four stroke engines have some level of super charging. They build up stored air under pressure and release it in to the intake port directly above the combustion chamber.