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It really depends on the application...try both and see what the motor likes.

If you have a lot of cam or run a stick, many times the manifold vacuum can be used to get a little better idle.
 

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Discussion Starter #3
It's just a stock 460 in my f150.

The carb has all the other ports sealed. Just like to know before having to take the carb off and dig the silicon out of the ports.
 

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You'll get a better signal from port vacuum. Some people use the manifold vacuum port, to try and run a distrbutor vacuum advance. I don't know why. The port vacuum, is designed for the advance mechanism. IMO
 

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Discussion Starter #7
Am I correct to say that port vacume increase as rpm rises and manfold decreases as rpm rise?
 

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Vaccuum signals...

Ported vaccuum signal wil rise from "0" to the same as manifold vaccuum at about 15 degrees of throttle opening. It will mimick manifold vaccuum from there on up.
VENTURI vaccuum will rise as air speed becomes greater reguardless of manifold vaccuum.
 
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