High altitude, and low octane

[Kaklikian, Gary]

Brad, my understanding has always been that, due to the thinner air, lower
octane fuel is required at higher altitude. Consequently, 91 octane here is
roughly equivalent to 93-94 at sea level. 
The last time I was down at low altitude (700ft),  service station premium
was 91 octane and my 4000 detonated noticeably under load with it. This does
not happen with 91 octane here at 6000ft.
But,  the car responds very well to half a tank of 101 octane mixed in with
the 91 even at 6000ft - less hesitation, better acceleration,  and cooler
exhaust temps.

For an unmodified motor designed to run on premium pump gas, I'm not sure
how much benefit you would get from higher octane fuel. It may run rich if
you bump the octane up more than a few points. Once you start modifiying
boost levels, timing curves, turbos/intercoolers, etc ,  then  you will
likely raise the octane requirements of the motor. 
(When I was down at 700ft, the racetrack was selling 105 octane. I put in a
lot without cranking down the high boost fuel level and I heard a small
explosion in the exhaust when  I shifted.  A witness claimed he saw flames
out the exhaust  - no cat, but definitely not good for the O2 sensor.)  

Duggan's Petroleum off Sante Fe & Oxford in Englewood sells both 101 and 105
octane unleaded.  The 101 was $3.00 a gallon last week,  not outrageous
considering $2.00 for 91 pump gas.  
Mix in some 101 in your car and let us know what difference it makes. I've
noticed an improvement even adding just 5 gallons to a 17 gallon tank.

Gary Kaklikian
86 4ktq
92 S4


> ----------
> From: 	Brad Wilson[SMTP:bradw at pobox.com]
> Reply To: 	Brad Wilson
> Sent: 	Wednesday, May 30, 2001 7:25 PM
> To: 	Audi Quattro List
> Subject: 	High altitude, and low octane
> 
> Living in Colorado, we get 85, 87, and 91 (US-rated) octane fuel, rather
> than the traditional 87, 89, and 93 (though some sea-level gas stations
> use
> 91 octane for their premium).
> 
> Apparently, one of the local TV stations, KOAA[1] in Colorado Springs,
> had an exposé last week about this. The traditional story goes: the higher
> you go in altitude, the lower octane fuel you require. They claimed that
> while this is true of carbureted(sp?) engines, it's not true for fuel
> injected engines. (Of course, the major source of controversy here, too,
> is
> that we're paying more for 85 octane than others pay for 87, but that's a
> separate issue... just saw $2.10 for 91 octane today).
> 
> So, I figured this list probably has at least 1,000x the brain power of
> the
> average TV investigative reporter, and before I passed on the "electronic
> petition" link to all my friends, I thought I'd get the scoop.
> 
> The $64k question: for fuel injected cars, do you want lower octane fuel
> for
> higher altitude, or the same octane as cars that run at sea level?
> 
> ObAudiRef: I always use 91 octane. =) And there are occasional stations
> around (_very_ hard to find, and _very_ expensive) that offer 93 octane
> fuel
> here in the "high plains".
> 
> Best regards,
> Brad
> 
> [1] http://www.koaa.com/
> 
> 2000 A6 2.7 biturbo quattro   http://www.quality.nu/bradw/audi/
> 2 turbos, 1 driver ... no limits
> 
>