Newbie Audi owner, newbie question: Octane
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Joined: Jun 2004
Posts: 4
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Newbie Audi owner, newbie question: Octane
I just bought an Audi A4 1.8T with 25,000 miles for $16,000. Best damn car I've ever owned. I just realized though that you're supposed to put 91 Octane gas in the tank.
Does this really matter. Probably does I'm sure, but with gas costing $2.30/tank at that octane, I'm looking to cut corners...
Does this really matter. Probably does I'm sure, but with gas costing $2.30/tank at that octane, I'm looking to cut corners...
2nd Gear
Joined: May 2004
Posts: 1,096
From: Indianapolis, IN
RE: Newbie Audi owner, newbie question: Octane
Yes, it does. I know there a some on the forum that do not use the high octane fuel, but in my opinion it is important. The way our cars are tuned to run advances the timing for performance, thus requiring the higher octane fuel. Lower octane fuel tends to cause the engine to want to knock, thus the car adjusts by retarding the timing. So while it may run ok to the human ear, it's proabably not perforing to its capability. Welcome to the forum.
3rd Gear
Joined: May 2003
Posts: 2,659
From: United States
RE: Newbie Audi owner, newbie question: Octane
Ditto.
Here's an interesting quote that may shed some light.
Here's an interesting quote that may shed some light.
Regarding Octane and MPG:
Low octane fuel will effect max power on most new cars. Cars that require full power most of the time (exotic sports cars, etc.) will get better mileage with higher octane fuel.
Higher octane will only help power or efficiency if the fuel you are presently using is too low to allow ideal timing and air fuel ratio. In fact, because of slightly slower burning of higher octane fuel, you may actually get slightly worse efficiency when using an octane rating higher than required. Higher octane fuel is not necessarily better for the engine since the computer will protect the engine from damage from all but extremely low octane fuel. All gasoline engines only require their rated octane when running at fairly high power settings. In the past, before computer engine control, the engine would knock when pushed hard using low octane fuel. On most modern engines the compression ratios are too high to run at best efficiency at WOT on the rated octane. The computer retards the ignition and/or richens the mixture to allow WOT without detonation, but this reduces the efficiency and mileage. However, since most cars run at a fraction of WOT, it is unlikely that octane will have much effect on mileage.
If you are commuting most of the time and don't need the full potential of your car you can save some money by using low octane fuel. If you then want to get full power again you will have to run high octane for a while so that the computer can re-adjust the timing and fuel curves. You can't switch to high octane and expect the car to have full power immediately.
By the way: In most of California the highest readily available octane is 91 so the switch to 89 is not as significant as it would be when going from 93 octane.
Low octane fuel will effect max power on most new cars. Cars that require full power most of the time (exotic sports cars, etc.) will get better mileage with higher octane fuel.
Higher octane will only help power or efficiency if the fuel you are presently using is too low to allow ideal timing and air fuel ratio. In fact, because of slightly slower burning of higher octane fuel, you may actually get slightly worse efficiency when using an octane rating higher than required. Higher octane fuel is not necessarily better for the engine since the computer will protect the engine from damage from all but extremely low octane fuel. All gasoline engines only require their rated octane when running at fairly high power settings. In the past, before computer engine control, the engine would knock when pushed hard using low octane fuel. On most modern engines the compression ratios are too high to run at best efficiency at WOT on the rated octane. The computer retards the ignition and/or richens the mixture to allow WOT without detonation, but this reduces the efficiency and mileage. However, since most cars run at a fraction of WOT, it is unlikely that octane will have much effect on mileage.
If you are commuting most of the time and don't need the full potential of your car you can save some money by using low octane fuel. If you then want to get full power again you will have to run high octane for a while so that the computer can re-adjust the timing and fuel curves. You can't switch to high octane and expect the car to have full power immediately.
By the way: In most of California the highest readily available octane is 91 so the switch to 89 is not as significant as it would be when going from 93 octane.
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