Octane rating
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An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without undergoing pre-ignition. The higher the octane number, the more compression the fuel can withstand before detonating. Octane rating does not relate directly to the power output or the energy content of the fuel per unit mass or volume, but simply indicates gasoline's resistance to detonating under pressure without a spark.
A US gasoline station pump offering five different (R+M)/2 octane ratings
Gas stations have gasoline with different octane ratings. Higher numbers indicate that the fuel can better avoid unintended combustions within pistons.
A 1940s US propaganda poster using the term "octane" to emphasise power.
Ignition timing
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In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke.
Timing light