Actually looking into the whole octane business, one will learn how and why we have different grades of fuel for different engines. Turns out higher octane fuels were needed as engine efficiency improved. Lower-octane fuels will combust at a lower pressure without a spark being applied, so in a high-compression engine, a low-octane fuel will ignite in the cylinder before the piston hits TDC, which is not good for the engine at all, and it's lousy at providing power to the crank, as well (as long as the engine holds together, that is).
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