soilsampledave

I just picked up a well used 2001 A6 2.7t. I see that the manual calls for 91 octane. I think I will be better off with the 90 octane pure gas that I can get nearby versus the 92 or 93 octane premium with ethanol I can get everywhere else. Seem right to the experts around here?

A4 Phil

Hmmm...I was traveling to NY (Upstate) last spring and saw a gas station offering 'real' non ethanol mixed gasoline and I pulled in. I was almost empty, though not on fumes. Anyway, filled the tank and was saddened by how much power I had missing out over and simply forgotten about...and my gas mileage improved over that tank of gas (I know, not scientific.)

I would run a tank of real gas and if there is no knocking, you are in business. If you are worried, fill with the 90 and have a bottle of octane boost on hand if you get worried after running on it. However, you will not do any damage running 90 octane.

I would kill to have a 90 octane real gas service station around NoVA. Please!

feirstein

Post makes no sense. 10% ethanol does not reduce power at all. If your fuel meets min octane requirements it will produce the same performance as 0% ethanol fuel. Octane is octane.

However, MPG's will take a small drop on 10% ethanol.

lucio_liu

I can maintain the MPG by fueling shell plus(89 octane) if I drive my audi like grandmother, no problem, no knocking.

I have tried pure 93, pure 89, half tank 87 half 93. at all major brand station.


definitely shell 93 is the best in Texas, I can tell. but if you want to save money 87/93 mixture will not hurt.

twentysevenlitres

Ooh, no sir! Octane is not Octane!

Your fuel (USA) is measured as an average of two Octane Measures
RON is measured in an engine under no load and basically gives a figure of how well the fuel burns.
MON is measured in an engine under load and basically gives a figure of how much work the fuel can do - or how well it performs.

10% ethanol blends give a poor MON figure - you do not get as much work out of them.
They do raise RON though, which can help reduce knocking, but mainly they're used to reduce emissions.

SloopJohnB@mac.com

Turbo cars probably more sensitive to lower octane than the non-420hp 4.2 V8s. During the last couple years of storms out East I had to run the 2K4.2A6 and the 02S6 on 87 octane regular. I didn't hammer them, but they ran without knocking. Therefore without full throttle use I couldn't tell a performance decrease...
As soon as power came on at the local stations they had ran out of premium...or were only taking regular into the tank(s) for the duration, about a week (derecho out east plus Sandy). Ran the Audi car tanks to the dash light and refilled with 93 (R+M)/2 Shell and all was well.

feirstein

Ethanol is not added to reduce emissions, it actually can raise certain emissions. It is added because the corn lobby is very powerful and the previous presidential administration was wrong to bet on ethanol as a strategy to reduce the U.S.A.'s dependence on foreign oil.

But octane is octane, just make sure to compare apples to apples (the same measuring technology). Again the dual method selected in the U.S.A. was driven by a desire to make testing twice as expensive so that compliance testing would be too expensive. Major fraud was a big issue and many States bit the bullet and now have the authority and funds to do compliance testing. Again the lobby guys with money and influence got their way.

GTA_Driver

The only difference 10% ethanol fuel will do is deliver 3% less mileage so if you normally get 300 miles per tank on pure 91 gas, you will get 291 miles on 91 gas with ethanol.

In theory anyway. In my experience, i did not discern any difference in mileage between ethanol and ethanol-free gas.

Also, while most stations here in Canada add 10% ethanol to fuel, some stations only use 5% for mid-grade 89, and no ethanol for premium 91. Then, other stations add 10% to all fuel trims.

Bottom line - don't worry about it. It will make no difference to your experience.

Also, i ran my 4.2 a6 (2001) on 89 in the winter regularly with zero engine knock. Sometimes in the summer too.

Just recently i tried 87 in my Allroad that's tuned for stage 1. No issues unless i floor it. Then i heard knocking. Did that as an experiment. Reduced power, since the engine retards timing. So not a good idea. Drive it moderately an it's fine.

Ran on 89 without issues.

Of course, i normally put 91 since it's tuned, and sometimes 94 for extra kicks.

A4 Phil

Hmmm...have you run real gas recently? I think you would be surprised to find out what you have been missing out on, power and MPG wise.

SloopJohnB@mac.com

Check your facts.
Here's one source.
http://www.afdc.energy.gov/vehicles/...emissions.html