My head choice dilema...

[MiracleMax]

Originally posted by jimberg:
Just so you know what kind of time spans we're talking about here. At 1000 rpms, it takes the crank .06 secs to make a revolution. If advance is at 10 degrees it's about 0.0017 seconds of explosion time we're talking about. At 6000 rpms, it would take 62 degrees of advance to allow that much time, but with the speed and heat being generate, total advance can only be little more than half of that.

don't forget though, combustion chamber shape and volume, rod/stroke ratio, spark plug location, piston shape, ect. effects the total timing needed

I had a shop teacher adamantly maintain that no engine could be revved past 6,000 rpm or so (yeah rite!) since his calculations were based on a steady state burn (gasoline),
unfortunately he didn't any other variables in account when he did the math!

For a high RPM engine, a small chamber with a good R/S ratio is desirable, along with a port/chamber design which promotes good fuel atomization/homogezination.

a. a small chamber reduces the time it takes to burn the A/F mixture across the chamber
b. a high r/s ratio creates more piston dwell time at TDC
c. highly atomized and homoginized fuel tends to burn more rapidly.