To Vacuum Advance or Not to Vacuum Advance

I did a lot or reading on this and recently added vacuum advance to my 68 340 (actually 372 CID) Cuda. I run it off of the manifold vacuum and am running a pretty good sized cam that creates low manifold vacuum (252/257 @ .050) at idle. The slight increase in advance at idle (if any) allows you to close the throttle plates and square up the idle transfer slots on a Holley carb (if you are running one) and helps clean up the idle. Once off idle and you are accelerating there isn’t really any manifold vacuum so it doesn’t add to the total advance. When cruising or decelerating you get the benefit of additional (vacuum) advance which cleans up emissions and improves fuel efficiency.

I can say that it has made my car much nicer to drive on the street.

Of course you need to set your mechanical advance curve (lightweight mr gasket springs in mine) set your total mechanical advance (I welded up the slots in my stock type electronic distributor after the initial was set to limit the total mechanical advance) and adjust the vacuum can as needed.

Just sharing what worked for me, lots of folks also have luck with a ported vacuum source.