KJL

I know manifold vacuum goes to zero at WOT and ported vacuum starts at Zero but as the throttle blades are openned, vacuum increases. Does ported vacuum drop off at WOT? My guess is it does not. Lars tech article states that max performance at WOT will be had at 36 to 38 degrees total advance. This would be covered by the mechanical advance alone. If you add the vacuum advance to this , you would be at 50+ degrees total at WOT!
Something to think about. You can run manifold vacuum but some engines will not like a lot of advance to soon. Mine seems to like it. :D

sb69coupe

Ported vacuum is only present in part-throttle situations. When the butterflies in the throttle body open further, the venturi effect is reduced and the vacuum at the port diminishes.

lars

As soon as the throttle blade is cracked open to expose the ported vacuum port, the ported vacuum acts exactly the same as manifold vacuum. There is no ported vacuum at WOT, just like there is no manifold vacuum at WOT.

KJL

Thanks for the help!!