In a message dated 06/12/2000 10:41:13 PM Eastern Daylight Time,
mikech@sprynet.com writes:
<< Waste of money. If your car is not designed or altered to need it, high
octane has no benefit. High octane fuels are designed for engines with very
high compression ratios or forced induction (racing engines, aircraft, etc.)
. High octane is not necessary at the compression ratios stock Spitfires
run. A quote from Sportbike Performance Handbook "The value of high octane
fuels in unsupercharged engines lies in the higher compression ratio they
will tolerate without detonation. Simply replacing a lower fuel with a
higher does nothing for power. Essentially, the octane number measures the
temperature stability of a fuel molecule. To obtain the value of a higher
octane number, the compression ratio must be raised."
If your car is not pinging or detonating on the lower octane fuels, a higher
one is just a waste of money. In fact it can and will reduce power in a
lower compression engine. In small cylinder bore engines, such as the
Spitfire, higher compression can be run with lower octane numbers because
the distance the flame has to travel is smaller. I've used nothing but the
87 octane fuel in my 9:1 Spitfire with no problems at all. Just use the
lowest octane you can without hearing pinging (sounds like coins in a jar).
>>
You missed one benifit from using high octane fuel, it burns at a slower
rate, giving you better MPG! I get between 15-20 more miles out of a tank of
gas using high octane fuel, than using the low octane fuel. It's well worth
the extra money to me!
John C. Smith
75 Spitfire "Bad Mojo"
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