quote:

ORIGINAL: Tahoe SC

now why would a car designed to run on 87 require higher octane?

it's possible that due to age, there is enough build up of carbon deposits, etc. within the cylinders to increase operating temps dramatically, pressure, etc. lower octane fuels in this environment would combust even before TDC due to the high operating temps...so you stick in higher octane and it makes the engine run much better.

i'm not saying this is what is up with BMG's bike, but just some possible answers.

anyone remember dad's old a$$ olds or buick that always pinged and ran like crap...and if you turned off the engine, crazy car would still sit there idling for a bit?

put high octane in there and it ran great...and we stood around and said...WTF? hahahahahhah

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A low octane fuel may burn all at once (detonate) or even be
ignited by hot spots or carbon chunks in the cylender and ignite too early.
Preignition and detonation cause severe wear and damage to the lower end of
the engine such as pistons, con rods and bearings. The high octane fuel
burns slowly and evenly and should be finished by the time the valve opens.
The higher octane also has a higher combustion temp. than the low octane and
will not preignite.
    On the other hand, using too high of an octane can burn valves. Because
of the slower burning properties of high octane fuels, the low octane
engines will open the exhaust valve before the fuel/air mixture has finished
burning and will elevate the valve and exhaust manifold temps causing
premature valve wear or failiure and may burn holes in the exhaust.
    So, the best thing to do is use the octane rating in the owner's manual

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There have been a lot of ideas thrown out there about this, so here's
another one.
Think of higher octane gasoline as a slower burning fuel. All things
being equal, it takes longer to ignite and longer to burn. Thus, high
octane fuel is desireable in situations where the tendency to knock
is high, such as high compression ratios and forced induction. In
essence (no pun intended), higher octane fuel needs more ambient heat
in order to start the reaction.
In order to make use of the higher octane fuel in an engine which is
designed for low octane fuel (while keeping the same spark plugs),
one must advance the timing--so that the spark plug fires a little
prematurely. In this configuration, higher octane fuel will generally
make a low octane engine feel smoother.
However with everything setup stock, you will gain nothing from
higher octane fuel. If you hear pinging and you cannot eliminate it,
then you should try a slightly higher octane--but only enough to
eliminate it.

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Effects of octane rating Higher octane ratings correlate to higher activation energies. Activation energy is the amount of energy necessary to start a chemical reaction. Since higher octane fuels have higher activation energies, it is less likely that a given compression will cause knocking. (Note that it is the absolute pressure (compression) in the combustion chamber which is important - not the compression ratio. The compression rati

< Message edited by bmg velocity -- 3/30/2007 6:12:12 PM >

_____________________________

Does not want to debate insurance co.'s or bad drivers for at least a decade or 10. Want to argue the merits? You are a one man show. Sorry no takers here.

(in reply to Tahoe SC)

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It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion). However, premium grades of petrol often contain more energy per litre due to the composition of the fuel as well as increased octane.