False statement?

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Well neither your statement nor the one post on JJ which says "vacuum at idle" for ported is really true.

MANIFOLD vacuum means just that, whatever vacuum is at the manifold

PORTED vacuum is generated by the opening of the throttle, acting in the venturi. It is least at idle, "starts to come on" off idle, and gets stronger as the throttle AND RPM goes up, but if you firewall the throttle, they usually drop off at WOT

There are a couple / three strategies...........

Not highway driven / no long trips many guys just don't USE vacuum

Some use ported........

Some use manifold

The manifold / ported crowd have been arguing for years. They require a somewhat different advance curve. Me? Ported, thank you very much
 
Actually "ported vacuum" is NOT from a venturi and is only available at off idle. The "port" for ported vacuum is a little hole just above the throttle plate when it is in idle position. As you open the throttle plate the hole becomes exposed to the vacuum under the throttle plate. Because the hole is located in a straight wall section of the throttle bore below the venture section, vacuum drops off dramatically once the throttle plate pulls much further above the vacuum port.
 
For what it's worth, I use manifold vacuum for my vacuum advance. Very happy with it.
 
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