DWC_2.7T

With premium pushing $2/gal again in SoCal, I filled up with 89 octane last week ($.10/gal cheaper). I can't detect any difference, and my mileage & power seem to be the same. Comments?

oskidunker

I haven't tried this in a while.Seems to me when I first got the car I noticed a difference but I was trying regular.My 98 A^ 2.8 worked fine on regular for two years then needed premium.

phred

use whatever octane you wish, within reason.

Probably best not to risk using regular, but midgrade is probably OK.

MrBits

The point of higher octane is resistance to detonation. That's how octane is measured, by running the fuel through a special calibrated test engine. The main factors affecting detonation are compression and timing. More compression => more power up to the point where detonation occurs. More advanced timing => more power up to the point where detonation occurs. Detonation is destructive to the engine. There is a very fine line between no detonation at all and a wrecked engine. This also explains why old technology engines in performance cars required "hi-test".

Modern engines often have Knock(detonation) sensors which detect detonation and retard the timing (hopefully) until the detonation ceases.

Theoretically then, you should be able to run any reasonable gas with no damage, just a loss of power and efficiency.

My choice is to run premium because the rest of the engine(specifically compression) was designed (optimized) to run premium. Therefore the timing has to be EXTRA retarded to compensate. Also it's what Audi recommends, and while I'm reasonably confident about this level of understanding. They may know other specifics which caused them to make their recommendation.

I hope this helps.

Bollinger

If you get 20mpg and drive 20,000 miles per year you use 1,000 gallons of gas per year. If you save $0.10 per gallon you save a whopping $100 per year in gas.

Why fool around for $100/year?

DWC_2.7T

$100 here, $100 there...it adds up. I do about 80% surface street driving so I only average about 17.5 mpg (actual). BTW, Steve, if you have any of those pesky c-notes clogging your wallet, I'll take 'em off your hands .

muhammadc

The only time I used less than 91 octane (usually use 93 or 94) was in CO where the highest available was 89 (traveling). One tank of that, and the fuel filter was nice and plugged up, causing the car to choke and hesitate... I really wouldn't run less than 91 octane fuel. Your $100/year savings could be eaten up quickly if you need to replace a fuel filter every 6 months and possibly a fuel pump.

DrHandball

More than likely you filled up shortly after the stations tanks were filled by their supplier's truck or while the truck was filling the storage tanks. The sediment in the tanks gets stirred up and is often pumped through thier filters and into your fuel tank.

89 octane does not equate to dirty gas. You could have filled up with 93 octane and if it was dirty then your filter would have been just as clogged.

The filter clogged doing it job protecting your fuel system from dirt.

DWC_2.7T

There's no relationship between octane and cleanliness

April

Just pulling the plugs to clean or replace them, will offset any "savings".

There are dual knock sensors to prevent premature detontation.