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Ported vacumn is generated by flow velocity thru the venturi of the carb.
That is correct. And intake manifold vacum will be right around o at wide open throttle where ported vacum will be high. Thats why ported is used so much as it will give more advance with more throttle.
In the 70's Ford used a thermal valve with 3 vacum hoses. One to ported vacum , one to intake vacum and the other to the dist. It used ported vacum for normal advance but if it ran to hot the valve would switch it to mamifold vacum which would give it more timing at idle and speed up the eng causing the fan to pull a bit more air. Once it cooled down it switched back to ported vacum. Ron
This is correct. The vacuum can has two ports instead of one. My car was originally setup the same way, but was changed at some point to just simply use the intake vacuum. The issue with the way it was setup originally is that the idle speed is "dynamic" based on how hot the engine is. At one point I tried setting it back up this way, it was strange, that's for sure.
383, Hemi 4-Speed, AlterKtion, D60
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