RE: Causes of detonation

[mmueller@es.com]

I had a problem that was likely detonation in my 200q20v when it was still
under warrantee. Audi forgot the spreader on an oil wiper ring when they
built the engine. The cylinder would accumulate oil which in theory
increased the compression. The result was consumed exhaust valves at about 4
a year. It took the dealership a long time to figure it out because they
never bothered to tell the mechanic about the oil problem. The problem was
discovered a few hours after I was finally allowed to talk to the mechanic.

	-----Original Message-----
	From:	Graydon D. Stuckey [SMTP:graydon@apollo.kettering.edu]
	Sent:	Tuesday, December 08, 1998 1:48 PM
	To:	Sargent Schutt
	Cc:	Glen_Powell@ne.3com.com; Linus Toy; Phil Ackley; Paul R.
Cole; a 200q20v list; a Quattro List
	Subject:	Causes of detonation

	On Tue, 8 Dec 1998, Sargent Schutt wrote:

	> When all is said and done, what are the most common causes of
detonation, and
	> how can they be avoided in high-boost applications? Plugs blowing
out (reduce
	> gap)? Turbo overspinning/ heat soak? Dirty/oily IC
(innards)preventing proper
	> air cooling? I was not running enough HP to bend a rod w/o
assistance of
	> another problem. I had detonation, and that's what overstressed
the motor. The
	> rod broke in the middle. Bent first (this furthers detonation),
then finally
	> broken? BTW, I am in San Diego - sea level, cool dry atmosphere.
And the oil
	> seal was going bad in the turbo, so there was a plenty of oil
blowing through
	> the cold side, and through the IC.

	I think Glen is right.  Detonation can bring even a very healthy
engine 
	to its knees very quickly.

	I suspect that all of the above suggestions can contribute to the
final 
	straw that broke the rod.

	High pressure fuel-air mixtures are difficult to ignite, so bad
spark 
	plugs would only cause a misfire.  What you had was not misfire, but
too 
	much fire.

	If the mixture gets too hot, it will detonate on its own.  I think
that 
	too much ignition advance produces detonation that sounds different
from 
	spontaneous detonation, but I'd have to check my texts.   I'm not
sure 
	you'd hear the difference in the cockpit anyway.  Bad fuel can cause

	detonation very quickly also.  I suspect you had a combination of 
	insufficient octane (and/or insufficient fuel), too much heat in the

	intake charge, and hot spots in the combustion chamber to initiate 
	combustion.

	Does that sound reasonable?

	Later,
	Graydon D. Stuckey
	No Audis!  :-(