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You're right in everything you said. Detonation is when some part of the mixture not around the plug is ignited by the pressure wave. The flame front from that ignition and the flame front from the spark plug ignition hit head on and thats your ping. Detonation normally doesn't put holes in pistons though, it normally destroys the outter part of the piston, by the rings, or scores the cylinders walls until it takes out the pistons. Pre-ignition normally leaves holes in piston tops. As for firing on the way up, thats absolutely correct. To get the most power out of an engine, you want peak cylinder pressure at 14 degrees AFTER top dead center. I know it sounds weird that I call out a number, but the way geometry works, every engine will make the most torque if the peak pressure is applied at 14 ATDC. *WARNING* MATHS AHEAD! At 1000 rpm, the crank rotates 6000 degrees every second. (1000 rpm == 16.6 rps = ~6000 degrees/sec). So if we want peak pressure at 14 ATDC and we set base timing at 15 BTDC, it takes 29 degrees at IDLE from spark firing to peak pressure. In seconds thats 29/6000 or ~.005 seconds (5ms). At 6000 rpm though, the crank isn't going 6000 degrees/sec, its going 36000 degrees/sec. Because your IDLE a/f ratio is completely different than your WOT a/f ratio, the flame speed is going to be completely different (a/f ratio is the largest factory in determining flame speed). I think the Z runs around 50 or 55 degrees max advance at WOT/MAX RPM, but hopefully this sheds light on WHY you need to advance the timing as the RPM increases. Its also why if you adjust your a/f mixture by getting your car tuned, you have to rebuild your timing map as well, because playing with a/f ratio messes with flame speed and changes the required timing point to make max power.
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12:54:00 03/17/14
