[67ChevyRedneck]

Originally Posted by 1LoC10

Not sure, ill wait for some input... i havent had any problems

I'm confused too, there have been several threads on this, one side is ported and one is not. I have mine hooked up to the PS and mine runs well too. Some say ported, some say full advance.

http://67-72chevytrucks.com/vboard/s...vacuum+advance

http://67-72chevytrucks.com/vboard/s...advance&page=2

This makes sense to me:

Sorry, this is just not correct. Vacuum typically decreases as RPM increases. At WOT if the carb is sized correctly there should be no vacuum

The simple answer to the question is that if you have a stock or near-stock cam, you should connect to ported vacuum as no additional vacuum advance is needed at idle. Ported vacuum is taken above the throttle butterflies, and so is less than manifold vacuum at idle.

If you have an aftermarket cam that's a little warmer, connecting the distributor advance to manifold vacuum will provide additional vacuum advance at idle which can improve idle quality.

Once the butterflies are open to any extent, manifold vacuum and ported vacuum will be virtually identical and so there is no performance/fuel economy/etc. difference - the only reason for additional advance at idle is to smooth out a lumpy cam.