Originally posted by rangulo
Motorman
I need some clarificartion to the explanation you gave us. Having high compression advances the time of combustion. Running a hotter plug like a 5 will also advance the timing. Lower compression and colder plug like a 9 will retard the timing.
If in florida we are at see level and the air is more dense;so how would you set the same motor up as far as compression and plug using your .018 head clearance theory?
Did you mean that in some cases motors can be run with stock head shimming and 40% as long as a 9 plug is used and a good operating temp?
This is what Top Gun 777 explains about compression ratio and plugs.
AFM
" A hot plug will advance ignition and a cold the opposite. Also we can advance ignition by making combustion chamber smaller ( it won't be direct , but increasing compression ratio will bring ignition earlier and in the mean time will give us more HP). This is why if you make combustion chamber smaller, you use cold plugs ( colder plug compensates ignition advancing due to combustion chamber volume decreasing)."