Detonation, the uncontrolled burning of the fuel air mixture. Causes massive and rapid pressure build up in the cylinders and prolonged detonation can lead to engine failure. This is common in the 98-02 legacy imports from Japan as they are turned to run 102 octane. Run 98 in nz closest we have and if in heavy traffic on a hot day don\'t push car too hard. Detonation sounds like a ping ping noise.