Ron, one way I've been able to dial in a couple of extra degrees of advance is to polish the combustion chambers. That pressure rise you refer to can cause a thing called "preignition" which generates a second flame front across the combustion chamber from the spark plug. A rough combustion chamber can lead to carbon buildup, which glows from combustion temperature and acts like a second spark plug. When the two flame fronts slam together, that's the "spark knock" people hear on an uphill pull. It can be extremely destructive- - - -causing a hot spot on the piston crown and blowing big holes in pistons. A totally smooth chamber resists the formation of those deposits. Those kinds of modifications should be reserved for competition engines with a projected lifespan of a few hundred miles- - - - -not for street engines that are expected to run tens of thousands.
Jerry
