What's called FAI fuel is only necessary in a couple of FAI events where absolute power is a determining factor. In CL this is for 2.5cc speed, in RC this is for Pylon and I believe one event in free flight. The sole purpose is to level the playing field as far as possible so that secret and probably dangerous fuels can't be used to gain an advantage. For all other events you run what you brung . OK, I think CL combat is now limited to a max of 10% nitro but basically in anything except those 3 events I mentioned there's no limitation on fuels.

Personally I'm glad I don't have to fly CL stunt using the rather silly AMA rules .