What is knock detonation and results?

Due to abnormal combustion arise noise from the colliding of the multiple flame fronts and the increased cylinder pressure that causes the piston, connecting rod and bearings to vibrate called knock detonation. Any abnormality in the combustion process has serious consequences in the power output, longevity and emissions generation of an engine.

The causes of knock can be:

1.    Excessive compression - increases pressure / temperature

2.    Not enough octane rating - fuel more likely to explode

3.    Wrong mixture - excessive heating / lowering effective octane

4.    Ignition timing - too much advance increases peak cylinder pressures a LOT

5.    Poor cooling - leading to high cylinder temps and pre-ignition

6.    Dirty cylinders - more candidate points for pre-ignition

7.    ECU/sensor fault - lots of options

 

Detonation causes three types of failure:

1.    Mechanical damage (broken ring lands)

2.    scratch (pitting of the piston crown)

3.    Overheating (scuff piston skirts due to excess heat input or high coolant temperatures)

This causes a massive and sharp increase in combustion pressures which can damage pistons, rings and even heads.

 

 

     Retarding the ignition timing will delay the timing of the spark, which also moves you away from your detonation threshhold. Most popular "power programmers" or "chips" increase engine power by advancing the ignition timing, and requiring you to run a higher octane fuel to avoid detonation. These work great, except the advanced ignition timing is NOT compatible with most superchargers, unless you're happy to run 100 octane fuel. In fact, many supercharger systems include an "ignition boost retard" that retards the ignition timing when it senses boost from the supercharger. This allows you to maintain stock performance while not under boost, yet still remain safe while the supercharger is making its boost (and power).