Crockett 999

Just putting together my mates 72/350. Vacuum for the auto should run from the carb right ? And vacuum for the dizzy from the manifold right ?

joe_padavano

The vacuum modulator on the trans requires straight manifold vacuum. Usually this is taken from a port directly in a manifold runner, but if you have a carb port that is straight manifold vacuum and not ported vacuum, that will work fine also. It doesn't matter where the hose is connected, so long as it is straight manifold vacuum.

The source to use for the distributor is subject to hours and hours of debate. The factory typically used ported vacuum and also required things like a thermal vacuum switch or transmission controlled spark (the latter for emissions control). Some people swear by ported vacuum, others by manifold vacuum. The initial timing will differ between the two. Frankly, unless you care about a completely original hose routing, try both and use the one that makes the car run better.

Octania

the other way around
though you may find that the car operates better with the distributor also run to manifold vacuum. Especially if you use an HEI ignition.

Running distributor vacuum from the intake was common in 1965. They started using ported vacuum from the carb [none at idle] c. 1968 and I believe that was driven by emissions concerns. Drivability may have suffered, and then they had to add a thermal vacuum switch to overcome the overheating at idle problem induced by the retarded timing at idle.


"The initial timing will differ between the two. Frankly, unless you care about a completely original hose routing, try both and use the one that makes the car run better."
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yeah, what he said