Ported vs Manifold Vacuum Advance for your Classic Car

We discuss the correct ignition vacuum advance source for your classic car and explain why and how it works!
#ignitionsystem #distributor #classiccars #mopar #gm #ford #ls #hemi #msd #carburetor #holley #dragracing #hotrod

[@peterolson8350]

You are absolutely right in what you say. Have also wondered why some "experts" think you should have vaccum advance all the time. If the engine needs more ignition at idle, the mechanical setting changes instead. The last thing you mention is also very important on an engine with a hot cam, idling will be even worse if the ignition also starts and "rocks" as well

[@craig8187]

There is a myriad of variables as to which vac take off is more suitable and it is always combination specific.
As a general rule I prefer ported vacuum but I always test straight vacuum aswell.
Whatever the particular combo works best with, is absolutely the right way to have it set up 👍

[@mooosestang]

Also when you close the throttle at high rpms, the ported signal will be zero. I've tried it both ways and my motor runs noticeable cooler with manifold vacuum. Probably less chance of burning an exhaust valve too.

[@TheRolfano]

Well if you want vacuum advance at idle because of a larger cam then you need manifold vacuum. Some set-ups do better on manifold. So it just depends on the amount of timing and where the engine wants it.