Early GM, Chevys, used manifold vacuum until the early to mid 1960s, Mopar and Ford have always used ported vacuum advance that I'm aware of shruggy
The major difference in using manifold vacuum advance it is advanced most at idle and then drops off as the vacuum declines to the throttle, ported vacuum doesn't start to work until there is airflow past that port work scope

Last edited by Cab_Burge; 02/14/18 03:57 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)