prager

Hello all, I've been running 93 in the ol girl..but as all of us are aware gas is getting way too expensive!! $3.09 a gal!!! Will running 91 be a bad idea? I know the engine was 10.6 : 1 from the factory, but after 100k maybe it's a little less..does anybody have issues running 91 or should I just keep it on 93?

MrGoodbytes

Car was designed to run of 87 if need be, it just loses some performance.

I'm running 91 right now until I can fix my rich-running condition. I might even go 87.

Car came from Colorado, where the PO was running 85 in it.

George95

I read in either the owner's manual or the repair book that 91 octane was recommended for the 3.6 and 93 octane was recommended for the 4.2. Y

RussB

From the link below: ". . . the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe."<ul><li><a href="http://en.wikipedia.org/wiki/Octane_rating">http://en.wikipedia.org/wiki/Octane_rating</a</li></ul>

MrGoodbytes

Bleh, ratings are the same across most pumps in the US.

87 - "Regular Unleaded"
89 - "Midgrade Unleaded"
91 - "Premium Unleaded"

My 90 V8 owner's manual says car will run best with 91 but can function at 87, it's probably just retarded a degree or two.

RussB

Carbon buildup in combustion chambers will often result in slightly HIGHER compression RATIOS in high mileage engines.

Compression PRESSURE, however, will of course decrease in high mileage engines, because of ring wear.

Some good points regarding gasoline octane in high mileage engines may be found in the last few paragraphs here:<ul><li><a href="http://www.automedia.com/High/Octane/Fuel/ccr20050501ok/1">http://www.automedia.com/High/Octane/Fuel/ccr20050501ok/1</a</li></ul>

32Valve

I live in 92 octaneville. Last weekend on my drive to Portland, I found 93 in Goldendale Washington. Filled there going down and back. My V8 has never ran better. My mechanic said the ECU has 3 different programs for varying octane levels. One note though, I add 1/4 oz/gal acetone. It works as a surfactant and increases atomization. I get a boost of power, better mpg and even a higher top speed: 155 confirmed with GPS (test run last fall). I'm gonna do another top speed test, now that I have the INMotion chip installed. Can't do it until I replace the crap H rated tires I'm now running.

Mister Bally

I used to own a 1987 5000 cs (turbo quattro) and although the manual &amp; decal said use premium, I basically switche to regular after the first year with absolutely no noticeable problems for the next 17 years. I currently have a '04 A8L with 4.2L v8 which also says use premium and I maybe put in one or two tanks of premium when I first bought it and then switched to regular and have never had any problems. It still flys when I press the gas pedal and I still get speeding tickets!

Finally, my 2001 Beetle turbo (1.8L) also say premium. Same story there.

I try to always use brand name fuel though such as Exxon, BP, Shell, Mobil, Marathon, Sinclair etc.

MrGoodbytes

I think modern cars avoid knock issues with timing adjustments.

20VT90q

One being, the computer is scaling the boost down because of the low test fuel(knock) and it's bad for the engine. That 4.2L engine in the A8 is pretty high compression (11.x:1)IIRC. I do agrea about puting low test in a non tubro 10v 5 cyl though.