Pro Mod Wad:

I have a question concerning predetination. Are you familiar with the term oil canning, otherwise know as oil contamination of the combustion chamber? If so, can you explain it clearly and tell me what causes this?

Thank you.
Kristin George

Kristin,

You got me on that one. I have heard the term "oil can" but never in regards to detonation. In some cases, after a collision a repaired body panel or floor panel in an auto body will slightly buckle and return to shape when the pressure against it is released and acts much like the base of an oil can used back years ago. It can also make a sound when it moves in either or both directions.

As far as detonation or pre-detonation, this is caused when the mixture of fuel and air in the engine cylinders ignites earlier than it should. This can happen for many different reasons such as poor fuel quality, advanced ignition timing, contaminants in the mixture, too much oxygen, too much compression which causes excessive heat in combustion areas, and various other reasons.

In a racing engine, compression and fuel quality are usually the problems. In a racing engine that is using Nitrous Oxide for the power adder, much like a supercharged engine, the cylinder pressures get very much higher than a standard engine, so detonation becomes a very damaging factor.

What is happening during detonation is a pounding taking place in the combustion chamber as if someone with a very BIG hammer is beating on the top of the piston repeatedly. This beating transmits from the piston top right down the connecting rods and into the rod bearings and crankshaft. It will crack pistons and/or piston rings and flatten rod bearings to the point were the safe clearances get changed and can cause rod and/or crankshaft damage and then engine failure.

Oil contamination becomes the result of piston ring damage and the loss of oil control or wiping action from the oil control rings. In a standard car engine this will create excessive exhaust smoke, oil consumption, spark plug fouling and generally poor performance. In a racing engine this will cause a DISASTER!

The mixture of oil, racing fuel, and lots of oxygen created by the heating of the Nitrous in the combustion chamber creates a cutting torch-like condition and will cut its way through pistons, connecting rods and even cylinder walls or sleeves. I have seen racing engines that a detonation flame has actually welded the aluminum cylinder head to the cylinder block and turned it into junk. This is why race engine builders and the racers that use their engines work so hard on having correct tune ups, use high quality racing fuels and the very latest in racing ignition systems so that they are able to get maximum control over the detonation problems.

Kristin, thanks for a great question and hopefully my answer helped you a bit.

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