ASG TECHNICAL CORNER: Spotlight On Engine Detonation

What is detonation and how does it affect your engine?
Detonation is the combustion of the remaining fuel/air mixture in the cylinder chamber. Detonation occurs when fuel is subjected to additional heat or cylinder pressure. The cylinder pressure rises beyond its designed limits and, if allowed to persist, detonation will damage the pistons. Even the best engine parts cannot withstand severe detonation for more than a few seconds at a time. If there is enough heat and pressure in the combustion chamber, detonation can begin to occur before the spark plug even fires, which would normally initiate the combustion. This other form of detonation known as pre- ignition detonation happens when the piston is traveling up towards a wave of compressed, exploding gas. These are the worst kinds of detonation conditions, which may bend connecting rods and destroy pistons.

What causes detonation and how can you avoid it?
Extremely high engine operating temperatures can cause detonation.
Engines that are operated under extreme load for extended durations can lead to detonation. To prevent this, verify the cooling system is operating efficiently and check for low engine coolant or a defective electric fan or fan clutch.

Lean fuel/air mixture can cause detonation.
Dirty or clogged fuel injectors can cause a lean fuel mixture. A restricted fuel filter or defective fuel pump can restrict fuel flow to the engine. The carburetor or fuel injection system should be checked for proper operation.

Advanced ignition timing can cause detonation.
If the ignition timing is advanced too far, the cylinder pressure will rise rapidly. Retarding the timing a couple of degrees will usually eliminate spark knock. Verify the distributor is timed correctly.

Knock sensors can cause detonation.
Many late-model vehicles have knock sensors that can detect engine knock and automatically retard the ignition timing to prevent it, allowing engines to operate in a safe tune and avoid detonation. Make sure the knock sensor is functioning correctly to safe guard against detonation.

Fuel grade can cause detonation.
Using lower octane fuel than the manufacture recommends may lead to detonation. Most factory high performance vehicles require higher octane fuel due to higher engine compression ratios. Check the owners manual for recommended octane requirements for your engine.

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