Power will not decrease with premium. Octane is only a measure of the gasoline's ability to resist ignition upon compression.

A gas rated 93 Octane means it will has the resistance to ignition upon compression of a mixture that is 93% octane and 7% heptane.

The reason that MPG would decrease in a modern fuel injected high compression engine with knock sensors when lower octane gas is used is that if the octane is too low, the engine will retard the timing to prevent knocking. This consequently results in an incomplete burning of the fuel and thus less of the energy contained in the fuel is efficiently utilized.

Regardless of the octane of the gas, one gallon of gas contains about 115,000 BTUs of energy.

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Ali Al-Chalabi

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