In addition if your engine retards the timing to prevent detonation, then it will not be harnessing as much of the gasolines energy content as it can and thus gas mileage will suffer.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record