Black_RS4

^ do you still have your talon?

Northerner

I just bought a 1.8T and have been told to ONLY run premium gas. Am I fine with regular?

K04-S4

What does the owners manual or the sticker on the fuel fill door indicate for the manufacturer recommended minimum octane rated fuel for use in your vehicle ?

Turbo cars such as the 2.7T with 2x knock, 2x EGT, 4x O2 sensors and chipped ECU code that supports higher octane loves the higher octane fuels so it somewhat depends on the ECU programming. I don't run the daily driver 2.7T or the 3.0 on anything less than 91 octane. Once I was forced to run the 2.7T on a tank of 87 (country gas station only had 87) , the mileage and power went noticably down. FWIW, Audi recommends minimum 91 octane for both the 2.7T and the 3.0L.

I have flip switch ECU code for 100 octane and hoped to try it at the track this season, supposed to add another 30+HP on my current 2.7T setup.

Also, most higher octane fuels (91 vs 87) have better additives to help prevent your fuel system and valve train from gumming up over time, it burns cleaner and cats generally last longer.

986Jim

Yeah, if your chipped do NOT run 87 octane way too much boost for that octane level.


Technically it's impossible for the mileage to go down with regular gas, thats just in your head. Lower octante fuel has higher BTU value (by quite a bit) so a full take of regular WILL take you farther than 94 will. 94 or 91 octane has (especially 94) has a much lower BTU value and you will need to burn more of it for the same mileage.

Still with a chipped Ecu your stuck with 91 octane. Remember that at part throttle you could run 80 octane gas and it wouldn't make a difference, it's only at full boost you need high octane. So even with your 100octane program you could run 87 octane fuel, just don't floor it.

K04-S4

... and the fuel mileage calculations that I have logged since vehicle was purchased four years ago.

Also note that larger turbo's and bigger exhaust slightly increased mileage compared to stock... except when you floor it


All depends on the code. There is no way I would test these theories with my car... inquire with any ECU tuner about mismatching an octane rated tank of fuel with ECU code and they will immediately void any and all warranties, specifically excluding responsibility for serious engine damage.

The twin turbo 2.7T ECU will pull timing based on increase knock from running lower than 91 octane fuel, so a lower octane fuel will produce less power due to less timing resulting in decrease of turbo engine efficiency.

Audi clearly states in the manual and on the B5 S4 2.7T fuel fill door "Minimum 91 Octane". The stock ECU code is written specifically for 91 as the minimum.

Personally, I would run nothing less than the minimum octane rating as stated by your vehicle's manufacturer.

nemohm

87 achieved the best mileage so far.
Calgary

K04-S4

Mileage is only part of the equation.

Do you plan on owning your 2.7T long ?

Racing Gasoline Comparisons

Note at the bottom of link...

"A higher octane slows the burn rate and conversely a lower octane quickens the burn rate. You desire a burn rate that will match the needs and characteristics of your engine so that you may produce the maximum amount of power, but at the same time retain reliability. It is better to error to the higher side of the octane instead of the lower."

nemohm

The only time I run full tank with 87 – the consumption dropped to 11/100.
It might something to do with the climate –elevation, humidity, temperature.

Higher octane could result unburned hydrocarbons that exit the cylinders;
what’s the harm (if any) on turbos and cats, one could only guess…

whoace

At times like these when gas prices are high, it is probably better for you to fill up with 91. Gas has a shelf life of 30 days and then the octane levels drop. When gas is expensive, not many people fill up with Premium so the 94 at the pumps might only be 93-92.