Thread: Problem with new ZZ4 350 Motor

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this vac. adv . thing has been discussed to death with no one agreeing on nothing, but I've always said do what ever the cam manf. and dist. manf. recommends and you would be ok. the part I don't agree with is I've read on here about how GM came from the factory mostly with ported vac. this is not true and has never been that I know of. all of the smog cars had manifold vac. and was reg. with switches and sensors at dif. times to adv. and retard the timing. didn't need ported vac. here is a diagram of a basic smog 350 motor. they had vac. at the dist. at all times while in hi gear. most people by-passed these switches and run the manifold vac. straight to the dist.