Alot of the cylinder setup have to have .250 spacer plate. 363 sphinix is setup not to run spacer. Even if its a long rod motor they have to have .190 plate to run 86 piston. Im running spacer on my 4mil esr 310 pv. I just seen a 4 mil 310 put down very close to 58hp and 37 torque on pump gas a couple days ago.