Ported or manifold Vacuum to Dist.

carb? Looks like this type of port is higher in the venturi (choke point) where as these ported pickups are lower....maybe the placement is key? Seems you would get tip in vacuum then it would get stronger as velocity increased past the port? I guess graph proves this wrong as throttle at 90 (WOT) produces same if not slightly lower vacuum using a standard location port right above the throttle blade.
Holley velocity sensing port placed high at choke point of smallest venturi diameter"...Vacuum for the diaphragm is supplied initially from one of the primary venturis. As rpm increase, so does velocity through the primary venturi, resulting in a progressively stronger vacuum signal..."

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pishta said

is ported vacuum really zero at WOT? I thought velocity through the venturi where the port is located would produce a vaccum, ala Holley vacuum secondary carb? Looks like this type of port is higher in the venturi (choke point) where as these ported pickups are lower....maybe the placement is key? Seems you would get tip in vacuum then it would get stronger as velocity increased past the port? I guess graph proves this wrong as throttle at 90 (WOT) produces same if not slightly lower vacuum using a standard location port right above the throttle blade.
Holley velocity sensing port placed high at choke point of smallest venturi diameter"...Vacuum for the diaphragm is supplied initially from one of the primary venturis. As rpm increase, so does velocity through the primary venturi, resulting in a progressively stronger vacuum signal..."

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i agree that the placement of the vacuum inlet has a part in ported vacuum response signal. You raised a good point.
If the ported vacuum inlet was in the Venturi it would have an increasing vacuum signal with increasing throttle opening.
I was discussing a ported vacuum inlet directly above the throttle plate used to not engage vacuum advance at idle, and to engage VA at part throttle. So when discussing ported vacuum, it is necessary to know the placement of the vacuum port or the vacuum response plot.