Another timing curve question
Well thanks but I usually keep my trap shut with builds that are way outside my own experience unless its something specific. I'll give you my .02 but take it for what it is.
I agree with YR on not using a vacuum advance that is all in at 8"Hg.
The way I see it, vacuum advance is best matched for lower load, low fuel density situation.
Lets say the car cruises at 16"Hg, 2800 rpm in 3rd gear, and considering that it has stock heads and cam that probably doesn't get into its happy zone until higher rpm, we wouldn't be surprised if it wants fuel enrichment around 8.5"hg or even 10.5"Hg.
So if the engine needs power enrichment at 8.5", then the extra timing for low density makes no sense to me. I could understand if there was a little bit of vacuum advance being used at the begining of power valve opening. But full vacuum advance at the power valve opening or rod step up, is clearly mismatch.
What I'm thinking of is one light spring and one heavy spring with a loop. So I can crank it at about 12 degrees, and have it immediately advance once running to the start of the heavy spring, 26 or 28 degrees maybe?
That's basically what Direct Connection was doing with the tach drive race distributors.
They didn't care if the idle rpms were a little unstable.
Easier to deal with on a 4 speed even on the street. With an automatic when its shifted into gear at idle, it loses some rpms. Right? When losing rpms causes a timing change, it then loses more rpms, until it either stablizes or dies.
