[chiphead]

I've got a PI distributor in my car. To make it easier on my brain, I tweaked the Y axis so KPA easily corresponds with vacuum. The KPA values are about 2" of vacuum apart from each other.

So from 36 KPA, its about 19, 17, 15, 13, 11, 9, 8.5, 6, 4, 1" of vacuum as you move toward the top of the Y axis. Makes it easy for me to correlate to the vacuum gauge. If you notice, I pull all the vacuum timing at 73 KPA, which is about 8.5" of vacuum. That's about where my power valve opens. So it drops the vacuum timing, the PV opens and I'm rich and retrded as I approach WOT.

For the vacuum advance, I copied the behavior of the aggressive advance cans from a late 60s distributor. The vacuum timing starts at about 8" and comes all in by 15" of vacuum. At 15", it adds 12 degrees of timing. There are some cells where it deviates, mostly around peak torque and high RPM cruise where I was being careful with the tune.