Bit of a discussion if we can about detonation in the engine.

Why does it occur?

How can you prevent it?

Just changed to a bigger turbo and getting quite a bit of det under full throttle.

Now just in theory why is this and what needs to be mapped to prevent it. Richer/leaner, etc. etc.

 

Normally detonation is caused by either incorrect timing,fuel grade,fuel mixture (too weak) or excessive carbon deposits on the piston crowns(causing hot spots that glow after the ignition cycle).
If you are running a BIG turbo then it is possible that you are forcing a lot more air in causing the mixture to run weak.....it sounds like your fuelling needs looking at but i stand to be corrected


You just can't stop fiddling can you Jon!!

steve.

 

well it's not running lean, but more air means more cylinder pressure upon ignition, which is just the same as running more boost.

Jon, I also think your new turbo has an uprated actuator leading to more boost overall which is what we saw on the road.

Ultimately detonation, as apposed to pre-ignition, is cause by spontaneous ignition of some portions of the inlet charge, before the flame that started at the spark plug reaches it. This leads to big pressure spikes which cause the noise. The cause of spontaneous ignition of the carge can be hot spots, temperature of inlet, the temperature caused by rapid pressure increase, poor ignition and flame propagation and more I can't think of or never hear of!

Getting rid of it can be done by retarding ignition, to prevent the pressure rising too quickly. Increasing octane of fuel which increases resistance to self ignition. Decreasing the flame speed by fuel additive (some octane boosters can do this) or poluting inlet charge (exhaust pollution, water, excess fuel etc). Reducing inlet charge temp, and therefore cylinder temps prior to and during combustion (better I/C, more efficient turbo, more fuel, WI, but better breathing can make it worse too ) . Lowering boost or decreasing breathing in some other way. Lowering compression.

Paul

 

Cheers Pavlo,i've learnt something as well !!

 

A massive topic that can't really be covered in a small paragraph...

Click here for a useful web site that should help to explain things...

 

Nice one thanks

 

Means get a better mapper. lol

 

Get a re-map sooner rather than later or you will need another rebuild/engine. In the meantime limit boost (ie right foot) to keep away from det conditions.

 

All sorted thanks guys