wwest

And think about this. If the ignition spark results in detonation, spark knock, then the A/F mixture was already on the "cusp" of detonation and thus delaying/retarding the spark would then most likely result in detonation prior to the ignition spark. In any case with spark knock (non-lugging) retarding the spark would not help.

Detonation is generally defined as simultaneous ignition of the ENTIRE A/F mixture volume. But nothing is absolute, spark ignition of a mixture that is already close to detonation can also result in a flame front that advances too rapidly.

wwest

Oh, now I see..

"...caused by (spark) ignition of the fuel before TDC?...

You're speaking only of spark knock, but the most detrimental form of detonation is the result of SELF-ignition.

But in any case if you're getting detonation co-incident with the spark then the mixture was likely already on the cusp of self-igniting.

drummin4fun

Ok, I see what you are saying, but doesn't an earlier spark alleviate both types of pre-ignition? I don't see how a richer fuel mix would cause the ignition to occur any later... and wouldn't a richer mixture then cause other problems in a high compression engine? I am not a mechanic, nor a mechanical engineer, so I realize that my understanding of current technology is a bit limited.

wwest

More gas in the mixture..MORE cooling..

Ask any GA pilot.

Same theory as DFI, vaporization (evaporative cooling) of fuel just as it enters the combustion chamber allows compression ratios of 12:1, even 14:1 in some cases.

wwest

If the engine's A/F mixture is already on the cusp of detonation BEFORE TDC and you advance the ignition matters will simply get worse.