Manifold Vacuum Experiment

The point about load and rpm is this.

We adjust for load mechanically, by opening the throttle plates ourselves. Spark control is a response to that, not an input.

What happens to vacuum when throttle opening happens? It drops. That's why it's called vacuum advance, because it advances when there's vacuum.

If you want advance on the bottom end, and you have vacuum, when you're transitioning from low rpm and load you can either use a vacuum advance can.... Or use advance weights or turn the distributor.

If you want retard during low end acceleration, you can use the vacuum advance.... or twist the distributors or use spring control to bring in the advance at low rpm.

If you want spark advance during wot, you're an idiot.

I'm not saying you can't use a vacuum advance to do these things. I'm saying, If y'all are using the advance mechanism to redundantly do those things, then it's not being tuned for when it works best: low load, moderate rpm situations. If you're opening the throttle, the vacuum is dropping and advance is too, so you're not gaining anything other than a starting point anyway.

But here's the biggest point: when does 'manifold vacuum' differ from 'ported vacuum'?
Basically, at idle and just barely off it. After that, they're basically the same. Any vacuum advance games you're playing are already happening once you're past the just-off-idle point. You're wasting your time.
Manifold and ported vacuum exists for systems that were designed to use it. Hooking up a Chrysler vacuum advance system to it makes no difference after the throttle plates crack open a slight amount. I challenge ANY of you to show me a difference in power/torque curves on a dyno. It's all in your heads.

Besides, I'm using this post to prove the point: do you really want to take advice from a user that can't figure out the quote functions?
:poke: