No knock sensors on a 1964 1/2 Mustang.

Mark

----- Original Message -----
From: David Beierl <dbeierl@attglobal.net>
Date: Monday, July 12, 2004 2:50 pm
Subject: Re: Fuel Octane, Additives

> 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"
>
>