Quote:
Originally Posted by Former_Boosted_IS
Huh? Decrease in performance? 100 octane fuel is no different than 93 octane fuel if you are running identical boost. We really need to put this as a sticky, but octane is nothing more than a measurement of its resistance to detonation, i.e. pre-ignition. The higher the octane, the more resistant it is to detonation. Why is that important? Well for two reasons:
1. You can run higher boost on race fuel (higher octane) than pump fuel because the fuel is more resistant to detonation. That is because the fuel will not ignite before the spark plug fires even with the higher IAT temps.
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If you are igniting before the spark plug fires then you have major problems.
Detonation happens after the spark ignites and causes a secondary pressure wave that disrupts the normal combustion process:
FYI......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.....not before.
Initial combustion at the spark plug is followed by a normal combustion burn. But for some reason, likely heat and pressure, the end gas in the combustion chamber spontaneously combusts and creates a secondary ignition point within the same timing window. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug.
Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition.
The two are completely different and abnormal phenomenon and are caused by different reasons.