Quote:
Originally Posted by Larry/car
Different RPMs will change the advancement, remember the centrifical advance of mechanically timed ignition. As the RPM increased the ignition advanced accordingly. I would think the computer also advances the spark according to a multiple number of inputs. Why are you concerned?

The optimal angle is constant (I think  assuming the plot of pressure is symmetrical but I don't know for sure that it is). The amount of advance needed to hit it accurately changes with conditions, that's all. I'm not asking how much advance is required to hit the optimal, I'm asking where the optimal is.
I think it's somewhere around 23 degrees ATDC, but:
a) First I want to confirm where optimal is,
b) Then I want to understand why it's wherever it is
That way I'll have my ducks in a row next time I need to explain why advancing timing (can) cool the engine, but I'd like to have this fact squared away in advance (no pun!).
Sure lots of opinions on chrome wheels and automatic transmissions on this forum compared to the amount of physics help :)
This article makes it sounds like 16 degrees is ideal, and the amount of lead varies to hit it:
https://www.jcmmachineandcoatings.co...ngcombustion/