[olddog]

Ok the more dense the fuel air charge the faster it lights. This explains why the vacuum advance is important for part throttle operation. It makes sense that the more dense the charge the closer the molecules and the faster the flame can travel. It also explains why you need to back off the timing in a blown application.

However if this were the main factor, then why did the old mechanical advance operate on RPM alone, when at WOT, and the fuel injection engines pretty much do the same thing. Volumetric Efficiency increases with rpm to a point and then drops off again. Take a stock 5.0 for instance, it quits breathing around 3800 rpm and VE starts dropping like a rock. Then the theory should be that as the rpm goes up and VE increases the timing should be backing off. Then at above 3800 rpm as the VE drops off the timing should increase again.

I'm not trying to be argumentitive here. I would like to understand this.