All good stuff, thanks for all the input. So is there a difference in vacuum cans for ported vs manifold vacuum?? Say like a stock points dist. in '70 was hooked to ported vacuum correct? Are the newer distributors ie: mopar performance electronic ones, firecore, FBO, set up with a different advance unit that is designed to use manifold vacuum? or does it basically just boil down to how much vacuum your engine makes at idle and what it prefers timing wise?
A vacuum can is a vacuum can. The only real differences are how much additional timing they provide, and what vacuum level they start to move at.
Most can have the vacuum level changed by using an allen wrench through the nipple to adjust the spring load on the diaphram. (A mity-vac comes in
very useful for adjusting this)
To adjust the amount of advance a physical stop needs to be added to the arm.
Otherwise, it's based on your specific engine's idle vacuum, how much mechanical advance your distributor has, and how much total timing you want.
