Detonation vs. Pre-Ignition

[starquest 2875]

that was a long, but very good information.

[Gatecrasher]

This article ought to be required reading for anyone looking to do their own tuning.

Thanks for posting it. This will go in my reference library.

[Kibwe Walker]

Thanks for the Advanced section. Great read.

[Kibwe Walker]

Someone should sticky this.

[Synchro]

Excellent read. Cleared quite a few things up for me. This should be required reading for *everybody*, not just tuners.

[TiM_natalie3kGT]

Originally Posted by Kibwe Walker

Someone should sticky this.

yes it was a very good article

Sticky

[mjannusch]

Sticking it...

[Jimmy Nuetron]

its amazing, if i read a text book at midnight, it doesnt stick, but i read this through sometime around midnight, and i think i remembered most of it, and it explains what happened to my dads snowmobile when he was runnin stock jets and our own homebrew ram air, there was aluminum all over the spark plugs..hmmm...

thanks for puttin it out there

jim

[mjannusch]

Originally Posted by Jimmy Nuetron

...it explains what happened to my dads snowmobile when he was runnin stock jets and our own homebrew ram air, there was aluminum all over the spark plugs..hmmm...

You may have hooked up your ram air and forgot to pressurize the float bowls from the airbox... Without doing that, the ram air pressure will tend to hold the fuel down in the bowl and not allow as much up through the jet/needle. Going a size or two higher on the main jet is probably a good idea anyways, at least until you determine that it runs too rich.

[Import Power]

Originally Posted by klamathpro

So according to the above info, detonation most likely occurs in places other than the dead center of the chamber, thus running colder plugs doesn't help that much for true detonation and definitely doesn't draw or pull away heat from the chamber or anything silly like that. Colder plugs prevent pre-ignition which occurs 160 - 180 BTDC and possibly detonation induced pre-ignition because it minimizes the plug from becoming a heat spot. This is apparent from this thread showing detonation occurring away from the center.

Your summation is incorrect. One of the main jobs of a sparkplug aside from igniting the mixture is HEAT REMOVAL from the chamber. It is this HEAT (along with pressure) in the chamber that causes detonation. The colder the plug the more heat (and faster) the plug can pull out of the chamber and move it to the cooling system for removal. This chamber cooling is what colder plugs are all about. And this is why colder plugs lower chances of detonation.

Colder plugs also pull heat off thier tip faster which does help pre ignition as well.

Originally Posted by klamathpro

Key Definitions

Detonation

Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug.

Detonation
Unburned end gas, under increasing pressure and heat (from the normal progressive burning process and hot combustion chamber metals) spontaneously combusts, ignited solely by the intense heat and pressure. The remaining fuel in the end gas simply lacks sufficient octane rating to withstand this combination of heat and pressure.