Brand of Gasoline

[Mark Rosenkrantz]

Grant, modern engines adjust timing VERY rapidly, to lower emissions as
well as improve fuel economy.  Today's engines aren't static like a "single
map" or a "jet" in a carb.  It's dynamic, within parameters.  Modern "maps"
are ranges, not a static line.  As such, it's certainly plausible to get
a SMALL percentage of improved MPG under normal driving conditions.  Your
PV=NRT (I love the ideal laws!) and logic is only accurate if we squeeze
all of the power out of the incoming fuel.  No variation between slightly
rich as a "fudge factor to stave off detonation as an engine wears" or
running lean of peak, something which is used to get the combustion chamber
hotter, faster.

Now, the likely scenario is that she got ethanol-free gas.  As stated,
ethanol have less BTU's per volume, and will decrease your fuel economy in
ANY engine.  Another thought, which may be quite wrong.... but if the
engine maps can't handle it because it's so far out of parameters, this
would severely limit fuel economy by reverting to a very "safe" map in the
ECU.  Honestly, I forget what car, what altitude (air density), etc.

Do I believe 50% better economy in a "decently running car," no, I don't.
But if you told me by switching brands and going to ethanol free fuel...
I'd absolutely believe double-digit improvement as a percentage.

As an aside- get this-  In airplanes where we can adjust the mixture
manually, there is a growing trend to run the engine lean-of-peak
(significantly so).  GAMA has all the write ups you need if it interests
you, but the premise is this- high quality injectors and (this is key for
an air cooled engine) individual cylinder head temperature
(CHT) monitoring.  Over 10% increases in economy are the norm.  Pretty
awesome.  Of course, this is in a constant RPM engine... but the ECUs in
modern cars are adjusting multiple times per ignition cycle and are quite
accurate.

Mark Rosenkrantz

On Wed, Sep 19, 2012 at 6:55 PM, Grant Lenahan <glenahan at vfemail.net> wrote:

> No, not exactly. Read all my posts again
>
> Grant
> On Sep 18, 2012, at 8:29 PM, John Lagnese wrote:
>
> > Exactly!
> >
> > -----Original Message-----
> > From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com]
> On
> > Behalf Of Jeremiah Curry
> > Sent: Tuesday, September 18, 2012 7:02 PM
> > To: 'Jeff Waterstreet'; quattro at audifans.com
> > Subject: RE: Brand of Gasoline
> >
> > I am not expert, but isn't it feasible that with low octane gas in the
> tank
> > you go WOT, maybe to merge on the freeway, leading to detonation.  The
> > computer decides to retard timing.  Then the whole time you are on the
> > freeway the timing is retarded, leading to less efficient combustion.
> > Whereas if higher octane fuel had been used, that would not have
> happened?
> > My understanding is that the decision to retard timing will stay in
> affect
> > for some time.
> >
> > I am a convert to premium in vehicles that require it (my Allroad, MR2
> > turbo, and Triumph TR3) after having trouble with my 30v Passat and not
> > using premium.  However I agree it won't help on engines that don't need
> it
> > (my 80 series Landcruiser)
> >
> > Jeremiah
> >
> > -----Original Message-----
> > From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com]
> On
> > Behalf Of Jeff Waterstreet
> > Sent: Tuesday, September 18, 2012 4:17 PM
> > To: quattro at audifans.com
> > Subject: RE: Brand of Gasoline
> >
> > This discussion reminds me why the snake oil sellers and "magical
> magnetic
> > fuel savers" find people to buy their stuff.    Most people don't know
> how
> > to properly monitor their fuel usage, which is evident by many responses
> to
> > this topic.  I especially like those that say "my car just feels peppier"
> > when they run premium.    Two of my 8 vehicles require premium (one is a
> > 2001 A6Q 2.7T), and there is no difference in mileage between regular and
> > premium, unless driven very hard. (like towing a boat, with my other
> > "premium" eating vehicle, a Toyota Landcruiser)
> >
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