I was using a high octane (for colorado that is 91 due to our altitude.) in my
MG until I did a compression check. I don't need it. So I run 85 in it now.
(just plain old unleaded in Denver, Co)
If I understand correctly, the higher the octane, the slower the burn and
release of energy. If your octane is too low for your compression, then the
fuel burns too fast causing "pinking" when it pops. If your octane is higher
than what you need, it does not pink, but there really is no benefit because
the energy is released slower and the piston has already moved away from the
head. Too far away for the expansion from the burn to do you much good.
At higher altitudes, there is less oxygen, because of this, the burn happens
slower. This offsets the need for the higher octane.
My newer cars all require 87 octane. My feeling is that this is probably for
sea-level, and that I would probably do fine with 85 here in Co. They also
have computer controlled systems, so they are suposed to be able to adjust to
better use the higher octane fuel. I usually burn 87 in them because I have
noticed better gas mileage.
So, what altitude are you at, and what is your compression?
Andrew
On Fri, 26 Apr 2002, Paul Root wrote:
> I think we need to define what's what in the Octane rating for various
> countries.
>
> Here in the upper midwest of the US, pump octane ranges from 87-93. I
> know that's a combined number of two other different scales, and is
> obviously vastly different from England or Australia. I also seem to
> remember that regular unleaded in the Colorado Mountains is usually
> about 85.
>
> Can anyone clear up how the scales relate?
>
> Generally, I look for the mid-range 89-91 octane. That seems ok with
> the ZS. When I got to my SUs, I don't know what I'll do.
>
> Paul.
> '77B
>
> Ryan, Wesley wrote:
>
> > Which Brings up the question.....what are most people using for gasoline. I
> > have always used 97 octane from BP. Is that the best or is their better??
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