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I am working on a 440 six pack with with the Promax metering block. It does not have the fitting in the metering block for the normal vacuum line for the distributor. Now that port on a stock metering block is ported, correct? Meaning it does not get vacuum at idle but at throttle, correct? So, I should run the vacuum line straight to manifold vacuum, right.


Yes to the first question and a big NO to the second! The distributor vac advance needs ported NOT manifold vacuum. Manifold vac is high when the throttle blades are closed giving max advance until you open them up then it drops to nothing. This is backwards of the way it's supposed to work. Ported vac is higher during open throttle and nothing when it's closed. I can't comment on what GM did but this is the way Chrysler works. And to make it short the advantage in a street motor is it will apply vac advance before the rpm's get high enough to apply the mechanical advance. For a strip motor it doesn't make sense because as soon as the light turns it's full throttle and the rpms are up where the mechanical advance kicks in.

Last edited by Moparite; 02/14/21 01:33 PM.