Why does timing too advanced causes detonation?

[Holden]

Advanced timing increases cylinder pressures.

The more anything is compressed (pressurized), the hotter it gets.

Greg

[lundgren]

Compressed air burns faster. When you advance the timing, you ignite it early, and it burns so fast that it will totally ignite before the cylinder reaches TDC.

[SmokedSalmon]

I've heard that heat (due to lean) is the main cause of detonation, so why does timing too advanced causes detonation? thankx

[KevdoggLS]

So your saying that the spark actually happens before TDC?

-Kevin

[rjaffey]

The spark occurs before top dead center. The mixture is burning while the piston is traveling up, however the mixture takes time to burn and therefore it takes time for pressure to build up. Ideally the peak pressure is occurs at around 13 or 14 degrees after top dead center.

Too early a spark causes the the peak pressure to be too high and too early. This results in higher temperature and more heat transfer into the chamber wall, spark plug, valves and piston crown. The higher temp, higher pressure, and hotter surfaces in the chamber increase the chances of auto ignition (ignition of mixture not triggered by the spark) occuring resulting in secondary flame fronts. When the secondary fronts collide with that resulting from the spark, the result is a shock wave which produces the audible "knock" we associated with detonation.

[JRCivic]

Well said Rafe...


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'93 Civic Si H/B with B18C1, JRSC @ 8psi
Best 1320: 12.68 at 110 mph