If you have the late model MSD distributor you need the black (I think) bushing also, that shortens up the mechanical advance so you can have 18 degrees at idle(below when the springs kick in) and 34 or so at or above the RPM when the little springs stretch out. Make sure and check your total advance, don't run it higher than 36 or 37 degrees revved up, especially if it is on pump gas