No they definately are linked and pre-ignition is definately a pre-cursor to detonation.
Detonation is when the mixture inside the cylinder explodes rather than burn in a controlled manner. You can often get multiple flame fronts and lots of other nasties. Basically the temps and pressures inside the cylinders go up massively and can cause problems to the head gasket, pistons, piston rings, sparkplugs and all the bearings. Not good really!
Pre-ignition is where there is a hot spot that causes the mixture to ignite before the spark plug fires, this can lead to big problems such as trying to turn the engine backwards as well as localised heating, which in turn can burn out piston etc.
Pre-ignition can cause or exacerbate a detonation problem. But pre-ignition is far more dangerous to an engine than detonation. Detonation can be lived with for a while before an engine gives up the ghost, wheras pre-ignition can kill an engine very, very quickly.
Pre-ignition can be caused by all manner of things, from carbon deposits or anything that causes the engine to run hotter than usual. ie having carb heat selected at full power.
There is a phenomenon called "Detonation Induced Pre-ignition" so the two are definately linked.
One final thing. If an engine is detonating, what happens to the EGT?
It goes Down.
Last edited by Say again s l o w l y; 2nd Dec 2005 at 10:05.