Octane is a measurement of the fuels ability to resist ignition under compression. It's ideal to use fuel with an octane rating that is just on the edge of combustion so when the spark plug lights the fuel is ready. Too high an octane rating means the fuel is harder to burn than it should be
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Modern engines with close to 11:1 compression run just fine on 87 Octane and don't gain anything if you run rocket fuel.
