What crank angle should cylinder pressure peak at for max power?

[davepl]

There's some optimal point of leverage for the piston-rod assembly that peak cylinder pressure should occur at, but I don't know what it is and can't find it! Basically, if you graphed cylinder pressure, you'd want it centered over that point.

I'm not talking about ignition advance, although the amount of advance varies specifically to try to optimize for (by starting X degrees ahead of time, for example).

Anyone know what I'm talking about? I've found both 16 and 23 degrees ATDC cited, but neither with an explanation, and both can't be right!

[B. W.]

I know what your saying, but I don't know (I think you want it on the down stroke!) I do know it's dependent on many variables. It changes on a given engine based on fuel volatility & load. Googled it & found a paper "Cylinder Pressure in a Spark-Ignition Engine: A Computational Model". It has a formula, FWIW.
In my simple mind the easiest way to find it is to dyno the motor. The spark curve that produces the most power is where max cylinder pressure occurs at the optimal leverage point. OK, so you don't find the actual number this way but you know it there somewhere!