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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 

Does that sound reasonable?

Graydon D. Stuckey
No Audis!  :-(