I was always under the assumption that if it cost more, it must be better
for the car (after all...it's SUPER UNLEADED PREMIUM! Doesn't that sound
better for your car than Regular?)
Anyhow. Because Octane is a rating (in the US...Anti-knock index RON+MON/2
that you always see on the pump) is a way of calculating the autoignition
characteristics of the fuel ("I'll never admit to having Premature
Ignition..that girl was lying!").
Because fuel can be ignited by more than just the spark of a spark plug,
cars with higher compression and/or hotter running engines will be affected
by the auto-combustion of lower octane fuels.
Also note that if your car is not running up to snuff, e.g. extreame carbon
deposits can effectively reduce combustion chamber size, and retain heat
more than a clean engine making the car more susceptible to the premature
ignition/knocking.
And of course, what can cause carbon desposit build-up in your engine?
Running too high of an octane fuel!
Will switching back to a lower octane get rid of the carbon that has been
built-up in your engine? No. What will? Rebuilding your engine. (blah!)
For more information on GASOLINE than you ever wanted to know:
http://www.mr2.com/TEXT/gasoline_faq.txt
Section 6 is the most relevent to Octane calculations.
Terry L. Thompson
'76 Spit 1500
Maryland
----- Original Message -----
From: MikeC <mikech@sprynet.com>
To: Craig Smith <CraigS@iewc.com>; 'Spit list' <spitfires@autox.team.net>
Sent: Monday, June 12, 2000 10:37 PM
Subject: Re: Fuel
>
> 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).
> MikeC
>
> >burning Methanol. He said it was aviation fuel ! 140 Octane, he buys it
at
> >the local private airport, this caused me to think,,, what would a couple
> >gallons of that do in our 8 gallon tanks to the heads and valves or our
> >spits ?
> >
> >I would think it would burn very well if it didn't burn the tips off the
> >plugs or worse burn the valves clean out of the head.
>
>
>
|