[s-cars] S6 Mileage

[Cody Forbes]

There is simple science to explain this phenomena actually. Before I even start I'm going to stop the eventual flame fest by stating that the following is GENERALIZED and ROUGH FIGURES for the purpose of illustrating a point. If you want to know exact figures go do your own research and do not use my writings for your college thesis.

Ethanol's stoichiometric air:fuel ratio is about 9.0:1. Gasoline as I suspect the majority of us are aware is 14.5:1. Thus it takes about 30% more ethanol to run the engine properly. Gasoline is allowed to be sold without stating it's ethanol content (or that its got any at all) with a limit of 10% ethanol IIRC. At 10% ethanol the stuff in your tank has a stoichiometric ratio of roughly 14.0. Your oxygen sensor will notify the ECU of the car running a bit lean and the ECU will deliver the ~5% more fuel that is required to get the engine running at whatever oxygen sensor reading it's looking for.

Even more simply stated, your basic 93 octane with ethanol will net you roughly 5% worse mileage than 93 octane without ethanol. E85 with a good tune nets about 25% worse mileage. Don't jump too fast though... do you pay more than a 5% premium for ethanol free fuel? 

YMMV, to each his own, don't listen to me, I make this shit up as I go along, etc etc.

-Cody
(Sent from my phone, if a word doesn't fit blame Siri)

On Mar 26, 2012, at 11:37 PM, Larry <larrycleung at gmail.com> wrote:

> 3rd-ing this. No Ethanol free stuff within sane distance for me to experiment with though.  Do know it hit both cars about the same.
> 
> sent from my iPod
> 
> 
> On Mar 26, 2012, at 7:22 PM, "Steve Marinello" <smarinello at entouch.net> wrote:
> 
>> You're right, Tom.  The bulk of the mileage decrease also occurred after the
>> move to Houston, home to smog control and ethanol.
>> 
>> -----Original Message-----
>> From: s-car-list-bounces at audifans.com
>> [mailto:s-car-list-bounces at audifans.com] On Behalf Of Tom Heitzman
>> Sent: Monday, March 26, 2012 3:13 PM
>> To: s-car-list at audifans.com
>> Subject: [s-cars] S6 Mileage
>> 
>> After seeing Steve M's figure for mileage I came to the realization that I'd
>> forgotten the slow introduction of, but now, nearly, ever present dread
>> Ethanol into our fuel supply. I know that my vehicles get noticeably better
>> fuel mileage WO Ethanol. There are only two Ethanol free gas stations extant
>> in my general driving area, in Penn Yan & Utica NY. Both offer  89 Oct only
>> so I usually try to  have some 93 Oct in the tank for mixing. BTW If not
>> pushing the engine into full boost very often is 89 Oct OK w/MRC 2 or a
>> strict No-no? I've run it a few times and haven't heard any detonation but
>> my hearing is not the best!
>> 
>> 
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