What has to be remembered is PreIgnition CAN cause detonation, which will be
heard as knock. However, it can also be silent or at least it can go
unheard. Not ALL detonation is caused by pre-ignition. Preignition can be
caused by hot spots in the cyl OR too much heat/compression for the octane
of the fuel.(much less common - but possible. Take a 12+:1 stage 3 race
engine and run it on 83 octane fuel, and tell me it does not pre-ignite. It
will continue to run (when at operating temp) - real rough - with the key
turned off.) Anything that causes the fuel to ignite before the spark is
pre-ignition. Detonation is what happens when the flame front is not smooth
in its travel, and fuel starts to burn (uncontrolled) on its own . This can
happen sans spark, or after the spark plug has lit the charge.
A KNOCK occurs any time detonation is present - whether instigated before or
after the spark occurs has NO bearing on this fact. "Spark knock" and
"Preignition knock" may have a different audio signature, but they are both
detonation, and both WILL damage the engine.
----- Original Message -----
From: "Bruce A. Frank" <BAFRANK@...>
Sent: Tuesday, August 01, 2000 3:04 AM
Subject: Re: Knock Sensor ETC
> Pre-ignition and "knock" are not the same thing. You'll usually not hear
> pre-ignition because your engine is destroyed in just a few revolutions.
> The noise you hear is the rod coming through the side of the block. There
> is an excellent article in Contact! magazine on Pre-ignition and knock. I
> learned stuff that I didn't know that I didn't know.
> At 10:16 PM 7/31/2000 -0600, you wrote:
> >adpiccioni wrote:
> > >
> > > I figure one tappet out of adjustment would trigger the sensor
> > >
> > > alberto
> >The sensors are very selective - preignition has a distinct
> >sound signature that a loose tappet could not mimic.
> Bruce A. Frank, Editor "Ford 3.8/4.2L Engine and V-6 STOL
> BAFRANK@... Homebuilt Aircraft Newsletter"
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