ORIGINAL: Sport_Pilot
I think gear reducers are allowed for the advanced class.
Timing the ports for slower operation would be helpful when you compare it to what a nomal JET engine is timed for. The Jet engines are for small props and you want a bigger one. But of course you don't want to go too far with that. I would think the timing of the Fox engines would be about right, but with more exhaust duration to allow more power increase when using a tuned pipe.
You're right, it does indeed say so. I saw they were prohibited in another class and must have thought I was reading the advanced section. Well then.. [8D].. that opens up some possibilities!
[I still think a Sport Jett .46 on a wide blade low pitch 11" prop would be a serious contender]