ported vrs manifold vacuum

[Sal Lubrano]

Trying to figure out the difference in timing when a vacuum advance distributer is hooked up to ported or manifold vacuum. When the distributer is connected to manifold it is getting initial timing plus full manifold vacuum timing. When the pedal goes WOT the manifold falls off but the mechanical picks up so it is a wash. When the vacuum is hooked up to ported all you have at idle is the initial timing. When you go WOT then you will have full ported vacuum and initial with the mechanical adding more as the rpm's come up. So while WOT you will have all three advances Ported vacuum, mechanical and initial adding up to a higher timming? If I am not mistaken doesn't ported vacuum fall to atmosphere at WOT? (Goes from 0 at idle then follows manifold)
I am guessing hooking up to manifold will give you a much better part throttle acceleration because of the full advance at an idle and a great cruising engine temperature. Could someone correct me and explain why you would use one over the other better. Thank you.

 

[charlief1]

Up to a point it goes low at first but as vacume increases with rpm so does ported. The biggest advantage to using ported is at light throttle you get more advance and at crusing more timing gets you more mileage.