Its currently in HB D8. I have used several diff clutch setups on it so far. the latest being a firioni 4 shoe set up. tried a losi setup 2 carbon's & 2 alum green & gold springs-that just killed it.so far it seems to like the hot bodies clutch & firioni best. has stock restrictor & shims. I thought about trying a GRP pipe but from the last few comments that might be a waste. has a grp #4 plug. I just hate to think this thing doesn't make any more power than what I'm getting out of it now.It has over a gallon of fuel through it now & just barley has any mech pinch but great compression. It just has no power on the bottom & its not very fast.