Re: Octane vs. MPG

["Patrick Buthmann" <patrick@xxxxxxxxxxx>]

> Uh, to be clear, high octane gas render more energy. Ignition of a highly
> compressed air-gas mixture results in more energy than the ignition of a
> less compressed mixture.

Actually, that's not the truth, whole truth, and nothing but the truth.

Higher octane gasoline actually burns slower than low octane gas, hence it's
resistance to knocking.
What you really want is the fastest burning gasoline (ie lowest octane) that
does not knock.

Assuming that an engine has identical compression and timing settings, a
lower octane gas will actually produce more power than a higher octane gas,
provided that neither fuel contributes to knocking.

If compression is raised (which requires a physical change in the cylinder
or head), then the potential for knock is increased, requiring a higher
octane fuel.  It's the increased compression which generates more power, and
not the increase in octane.  A similar relationship applies with advancing
the timing.


Patrick








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