Shave the head aka glowplug. If you ported it, this is easy so I wont explain. Does cause the piston pin to detach and a hole to occur in the piston, but you can get to 8-4 for prop. Equivalent to an 09. Black widows just had better fitting parts, wasn't that special except the tank had a 5 minute run and supported inverted. The parts place said they had .051 cylinder assemblies