Here is my additional input on this thread. Hugh and Mike are both correct
in their own way. Hugh is right as to the caloric value of high and low
octane gasoline is exactly the same. If you burn a similar amount of 100
octane gasoline and 50 octane gasoline, you get the EXACT SAME amount of
heat. The higher octane allows more spark advance or "fake compression
ratio" as Mike puts it to be ran on the engine, and if the engine is not
"set up" for it, no performance benefits are present.
Some additional clarification on Mike's statement. The gasoline sold to us
does not have iso-octane or n-heptane in it (or if it does, in very small
amounts). In fact, its a mixture of a huge range of hydrocarbons. The
rating of say, 93 means that the blend has the same knock resistance on the
variable compression ratio test engine as a test fuel composed of a mixture
of 93% pure i-octane and 7% pure heptane. As you noticed, there is nothing
mentioned about the heating value of the fuel (or the power of the fuel as
you guys put it) because there is no difference!
>I run 93 octane in my Imperial, with 14 degrees of
>initial advance, very little vacuum advance, and an
>average amount of mechanical advance.
Mike is trying to get as much performance out of his 440 as possible. This
is the right way of doing it. Use the best grade gasoline available, and
set the spark timing as high as possible. The result is a car with quite
competitive performance as both Mike and I have raced modern high
performance cars and have little problem keeping up with them!
D^2
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