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No, better to tune the engine to make use of the extra octane. Higher
CR, more advance, or better intake/exhaust can allow the engine to use
the extra octane and produce significantly higher power. High octane
fuel does not necessarily burn slower, it is just less prone to
auto-ignition.
Propane burns faster than gasoline and is 150 octane, on average.

I have had several vehicles over the years that produced enough extra
power (and therefore economy) on hightest to MORE than pay the
difference in cost. Being computer controlled engines, knock was never
an issue - I could likely have run the thing on Kerosene after it was
warmed up.

So why do we even sell low octane gas and the low efficiency engines
that can burn it? The cost of manufacture is within 1 cent from why
my guys tell me. A high compression motor is just a better motor in
every way. Corky?