Originally posted by IL Sean:
Originally posted by geoffct:
They automatically retard the spark (reducing power) if the ecu determines there is predetination (knock). Many modern cars do not audibly or noticably knock. The car can detect in less than 2 revs a knock situation, and correct it in the next spark.





I have been able to hear the knock when I ran 87 octain, so it wasn't able to retard the spark at all.



There is only a finite amount of timing that the PCM will take out when detecing knock. Also, the knock sensor is not the most sensitive sensor so I wouldn't depend on it in lieu of running the correct octane for your car.

Bottom line: Run the lowest octane you can get away with, without having any spark knock/detonation. Higher octane WILL NOT give you more performance, unless your current octane choice is too low to begin with.