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Contact! magazine, issue #54, had an excellent
article on detonation, often called "pinging", and pre-ignition. He states that
pre-ignition can actually occur as much as 90 degrees before TDC, which is why
the piston gets eroded or holed in just a few revolutions. The piston is being
pushed up against the pressure and heat of the burning charge. An engine can be
run continuously while pinging, and it will only cause some pitting on the
top of the piston. I used to adjust the timing on my cars so that I got a slight
ping under a load. Where detonation can be harmful is if it causes a hot
spot to develop which in turn can cause pre-ignition. Back issues of #54
are available at www.contactmagazine.com
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ISSUE 54
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