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#11

07-10-2018, 04:05 PM

shipo

Senior Member

Join Date: Nov 2008

Location: southern New Hampshire

Posts: 2,726

Quote:

Originally Posted by virgin1

No sir, but I did forget to define run-on or "deiseling" which happens on carburetted cars that still have a fuel supply avaiable after the ignition is shut off, but has "hot spots" that keep the fuel burning. Since the engine usually runs in reverse under these circumstances, THAT can ruin an engine in short order.
Pre-ignition, as I understand it, is the ignition of the fuel prior to the spark plug firing (we agree to this point) due to hots spots and/or low octane fuels used, and that causes the pinging. It's very hard on the engine bearing, etc, but I have yet to see or hear of an engine dying from it in just a few revs. A higher octane fuel would is less likely to be ignited under these conditions, hence reducing or eliminating the "ping."

Pre-ignition will destroy an engine in short order, regardless of what causes the phenomena. What you described is detonation, and yes, hot spots can and often were (in the leaded fuel era) a primary cause of detonation. In the case of pre-ignition, there is never any associated "ping"; pinging/detonation while an engine is operating is virtually always post spark event.

FWIW, I've run many dozens of engines to destruction on dynos during my tenure with three different auto manufacturers and have seen all of this up close and very personal (as in when parts start flying around).