Date: Mon, 12 Jul 2004 18:50:28 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Fuel Octane, Additives
In-Reply-To: <b47fedb465b0.b465b0b47fed@gci.net>
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At 17:22 7/12/2004, Mark Tuovinen wrote:
>My Audi calls for 91 octane fuel and I have observed over several years
>and varying weather/driving conditions that it does indeed get improved
>mileage and run better with 91 octane vs 87. Enough so to easily justify
>the higher fuel cost, the mileage difference alone more then covers the
>cost variance.
>
>with the higher octane fuel, and ran better too. In fact the 91 octane
>fuel burned so much better that it increased the idle speed and we had to
>readjust it. The differences were probably more noticable on the car we
>used then most people would see as it called for a minimum of 99 octane.
Or to put both of these things a different way, modern engine-management
systems with knock sensors were able to retard the timing enough that you
could get degraded performance instead of blowing holes in your engine? I
don't want to be dismissive but in all honesty it's hard not to. It's not
any sort of secret that engines designed for high octane (i.e. high
resistance to detonation, using the properties of the substance octane as
representing 100 on the scale (and then fudged around later somewhat)) have
to have that quality to work properly and until recently, to
survive. Likewise it's not in any question that a) engines gain nothing
from an octane number higher than they need under given circumstances,
which one hopes will be covered under the mfr's specification; and b) that
chemically speaking, gasoline with high octane properties has measurably
less energy per unit than gasoline with lower octane qualities.
But "premium" -- more to it (maybe) than octane. And there was certainly a
time when EFI systems that had plenty of octane number from regular gas,
didn't get enough detergent from it to keep injectors clean. Now they do,
in US anyway, because it's Federally mandated. But only enough to keep
them clean, not necessarily to clean them. So if there's a question in
this area, it seems to me that it's best to specifically dismiss octane and
look a bit closer.
thanks,
david
--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage," '85 GL "Poor Relation"
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