What is detonation in simple speak?

When the air fuel mixture in the engine goes bang before it should do.

What! Please explain...

Detonation is quite a complex subject and this article only suggests explanations in basic simple speak! A basic and brief part of an engine cycle...

Normal Detonation
Piston goes down Piston goes down
Air is taken into the engine Air is taken into the engine
Piston starts it's upwards journey Piston starts it's upwards journey
  Fuel and air goes bang prematurely
Piston reaches top of cylinder - ish Piston may not reach top of cylinder!
Spark plug "sparks" and ignites fuel Spark plug fires - may ignite remaining fuel
Fuel and air goes bang Last bit of fuel and air may go bang
Piston goes down Piston may go down
Car surges forwards Car sort of goes forwards/may blow up
Normal engine sound Tinkling / crap engine sound


What causes the fuel/air mixture to ignite before it is supposed to?

This can be a variety of things:

Reason Why? Cure...
Ignition timing
  • Too far advanced
  • Retard the timing
Air sent to cylinders too hot
  • Poor IC efficiency
  • Hot air drawn into air intake
  • Turbo inefficient
  • Improve IC efficiency
  • Replace turbo
  • Cold air feed to air intake
  • Fit Water Injection
Turbo inefficient
  • The boost pressure set is too high for this turbo. The turbo is operating out of its maximum efficiency range producing lots of hot compressed air
  • Upgrade turbo
  • Run lower boost pressure
Hot spots in the cylinder
  • Carbon build up
  • Sharp edges/burrs/protrusions
  • Overhaul
  • Porting and polishing
Lack of fuel/lean mixture
  • Insufficient cooling by fuel
  • Air fuel ratios rubbish
  • Add more fuel - larger injectors, increase fuel delivery pressure
  • Sort out you air/fuel ratios
  • You may need a replacement or ECU add on
  • Change the fuel filter
  • Replace the stock fuel pump with e.g. Walboro
Incorrect grade of spark plug
  • Spark plugs are not dissipating heat quickly enough
  • Run colder grade plugs
Poor quality fuel
  • Octane rating low


How do I overcome these?

To set your ignition timing click here

To reduce the air intake temperatures click here

Turbo inefficient - have a look at an upgraded turbo.

Hot spots in the cylinder - overhaul head and remove carbon deposits/sharp edges around valve seats is the definitive cure. To "help" remove these deposits - run Redex, Optimax and Water Injection. WI will have the added benefit of cooling the intake air temperature dramatically.

Lack of fuel - upgrade fuel pump, run larger injectors, fit a fuel pressure regulator, get the car setup by a professional, get an upgraded ECU or ECU add on e.g. Dastek, Apexi S-AFC, MoTec, Haltech, Autronic - have a look here

Run colder grade spark plugs. For an explanation click here

Poor fuel - put your hand in your pocket and buy super unleaded. Optimax is the highest rated RON petrol in the UK.

What happens if I get detonation?

Detonation can damage your cylinder head, piston, piston rings, con rods and bearings. Avoid detonation it's expensive.

How do I know if I get it?

You should be able to hear a "metallic tinkling sound" from the engine. Often referred to as men with tiny hammers! You should also notice a decrease in engine output power, as the ECU retards the ignition timing. The ECU takes in a signal from the knock sensor to determine when the engine is knocking i.e. detonating. Click here for pictures of the knock sensor.

What should I do if I get detonation?

Don't drive wildly i.e. loads of boost, loads of acceleration.

If your car is standard suggestions are:

If you've turned up your boost: