Impact of regular/87 octane gas on fuel economy?
06-08-2019, 11:41 AM
#12
AudiWorld Senior Member
So I drive a little more than 12k miles per year and since I bought the car I have gotten an average of 30.5 mpg so I use about 400 gallons of gas per year. At a price difference of $0.25 per gallon the cost difference between burning regular and premium is $100/year. After doing the math it really is not worth worrying about the $100/yr so I will probably just keep burning premium (even though I lease the car).
06-08-2019, 12:16 PM
#14
AudiWorld Senior Member
I've always read that language as saying "this car is designed to run on 91 octane, but if there is no 91 octane available or if your clueless younger brother accidentally fills it up with 87, our engineering team put in a lot of effort to ensure that this will not cause permanent damage and you don't need to get the car towed and your gas tank drained of 87."
How it is that people read that language as a licence to run 87 all the time is beyond me.
How it is that people read that language as a licence to run 87 all the time is beyond me.
06-08-2019, 12:56 PM
#15
AudiWorld Member
100% agree with you, but events can accord after purchasing, I'm in the camp for following recommendation...... mfd's, Doctors, lawyer's, nutritionist's, etc. even when the benefit are unseen. I don't think i could take OP conclusion seriously there were too many variables affecting the outcome, however, these are the kind of experiment that led to a control study exposing the VW diesel scandal.
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Tango-Romeo (02-18-2023)
06-08-2019, 03:10 PM
#16
AudiWorld Junior Member
I'm still stuck at $0.25 more per gallon, where I live its more like $0.70 more, but I just take that into consideration when buying a car like this, as I do with the maintenance costs (of course, I try to do most of that)
Costco has good prem gas for a great price, and Sam's Club has a great price on non-top tier gas usually close to the same price as other's regular. I guess one does what one feels right for them. I've babied cars to death only to have them break down constantly and cars I did the bare minimum that were bullet proof, so ymmv.
Costco has good prem gas for a great price, and Sam's Club has a great price on non-top tier gas usually close to the same price as other's regular. I guess one does what one feels right for them. I've babied cars to death only to have them break down constantly and cars I did the bare minimum that were bullet proof, so ymmv.
06-08-2019, 03:48 PM
#17
AudiWorld Member
Thread Starter
I'm still stuck at $0.25 more per gallon, where I live its more like $0.70 more, but I just take that into consideration when buying a car like this, as I do with the maintenance costs (of course, I try to do most of that)
Costco has good prem gas for a great price, and Sam's Club has a great price on non-top tier gas usually close to the same price as other's regular. I guess one does what one feels right for them. I've babied cars to death only to have them break down constantly and cars I did the bare minimum that were bullet proof, so ymmv.
Costco has good prem gas for a great price, and Sam's Club has a great price on non-top tier gas usually close to the same price as other's regular. I guess one does what one feels right for them. I've babied cars to death only to have them break down constantly and cars I did the bare minimum that were bullet proof, so ymmv.
Going forward I will probably alternate between between 93 and 87 octane.
"They" say higher octane does not improve mileage. My experiment indicates the corollary is also (not surprisingly) true "Lower octane does not hurt fuel economy".
06-09-2019, 02:42 PM
#18
So I drive a little more than 12k miles per year and since I bought the car I have gotten an average of 30.5 mpg so I use about 400 gallons of gas per year. At a price difference of $0.25 per gallon the cost difference between burning regular and premium is $100/year. After doing the math it really is not worth worrying about the $100/yr so I will probably just keep burning premium (even though I lease the car).
I've always read that language as saying "this car is designed to run on 91 octane, but if there is no 91 octane available or if your clueless younger brother accidentally fills it up with 87, our engineering team put in a lot of effort to ensure that this will not cause permanent damage and you don't need to get the car towed and your gas tank drained of 87."
How it is that people read that language as a licence to run 87 all the time is beyond me.
How it is that people read that language as a licence to run 87 all the time is beyond me.
Even with that large of a price discrepancy that's less then $10 per week. Like AidanHadley said above, I'm not sure what people are doing in cars of this price point if fuel cost is of any concern at all.
06-09-2019, 05:12 PM
#19
From what I've researched, octane-increasing ingredients actually have (marginally) lower energy content than the base gasoline with which they are blended. From the test data I've read, the mileage difference is buried in the noise of the data, so your variation may just be on the high side of typical variance. But premium fuel certainly won't increase fuel mileage, as some believe.
The downside will be a lower resistance to knock, which will cause the engine to alter timing when knock-sensors detect it, slightly lowering peak horsepower. I don't have the exact numbers handy, but I recall that Lexus lowered both the octane recommendation and the horsepower rating of the engine in my daughter's car a couple of model years later, with no changes to the engine.
If you're on the track, at peak power for long periods of time, I'd recommend higher octane - for peak power/lap times/fun, and to avoid any issues with knock sensor overload (though I've never seen any data that backs up this concern). From an engineering standpoint, I believe using the minimum recommended octane rating is acceptable.
The downside will be a lower resistance to knock, which will cause the engine to alter timing when knock-sensors detect it, slightly lowering peak horsepower. I don't have the exact numbers handy, but I recall that Lexus lowered both the octane recommendation and the horsepower rating of the engine in my daughter's car a couple of model years later, with no changes to the engine.
If you're on the track, at peak power for long periods of time, I'd recommend higher octane - for peak power/lap times/fun, and to avoid any issues with knock sensor overload (though I've never seen any data that backs up this concern). From an engineering standpoint, I believe using the minimum recommended octane rating is acceptable.
From what I've heard, from a barrel of oil, you only can make so much gas and most of that is low octane. The super high octane stuff they do get is mixed with the lower octane stuff and then shoved into our tanks and money is then stolen from our wallets. But the point is that there is only so much high octane stuff available. So in areas with high concentrations of low octane burning trucks and people who will only use diesel, they have a surplus of said high octane stuff. In my crappy state (California) we have more people drive huge luxo SUVs that use high octane fuel, so we have a shortage of it and they take us to the bare min. But there is no octane ingredient other than high octane gas added.
Now I have no idea if high octane has more energy than low octane (I thought it was the same) but I can tell you that what the ECU will do when it detects low octane fuel is either lower the boost pressure or make the engine run slightly richer. So in the case of your Audi, it probably just keeps the boost lower. Problem is that some cars detect low octane fuel with a knock sensor, so knock has to be detected first and then it knows.. but knock at any time is bad for your motor. I know they do have octane sensors for the gas now but who knows... I wouldn't chance it, esp since I'm running a NS Power module and am loving the increase in HP.
Lastly, what car does the OP have? The Ultra A4 can probably survive much better on low octane fuel than the Quattro.
06-09-2019, 06:08 PM
#20
Permanent S Mode Member
Ok, I'm no expert but coming from a old JDM twin turbo car that was tuned within an inch of its life, you learn and pick up some things on octane and why you need it.
From what I've heard, from a barrel of oil, you only can make so much gas and most of that is low octane. The super high octane stuff they do get is mixed with the lower octane stuff and then shoved into our tanks and money is then stolen from our wallets. But the point is that there is only so much high octane stuff available. So in areas with high concentrations of low octane burning trucks and people who will only use diesel, they have a surplus of said high octane stuff. In my crappy state (California) we have more people drive huge luxo SUVs that use high octane fuel, so we have a shortage of it and they take us to the bare min. But there is no octane ingredient other than high octane gas added.
Now I have no idea if high octane has more energy than low octane (I thought it was the same) but I can tell you that what the ECU will do when it detects low octane fuel is either lower the boost pressure or make the engine run slightly richer. So in the case of your Audi, it probably just keeps the boost lower. Problem is that some cars detect low octane fuel with a knock sensor, so knock has to be detected first and then it knows.. but knock at any time is bad for your motor. I know they do have octane sensors for the gas now but who knows... I wouldn't chance it, esp since I'm running a NS Power module and am loving the increase in HP.
Lastly, what car does the OP have? The Ultra A4 can probably survive much better on low octane fuel than the Quattro.
From what I've heard, from a barrel of oil, you only can make so much gas and most of that is low octane. The super high octane stuff they do get is mixed with the lower octane stuff and then shoved into our tanks and money is then stolen from our wallets. But the point is that there is only so much high octane stuff available. So in areas with high concentrations of low octane burning trucks and people who will only use diesel, they have a surplus of said high octane stuff. In my crappy state (California) we have more people drive huge luxo SUVs that use high octane fuel, so we have a shortage of it and they take us to the bare min. But there is no octane ingredient other than high octane gas added.
Now I have no idea if high octane has more energy than low octane (I thought it was the same) but I can tell you that what the ECU will do when it detects low octane fuel is either lower the boost pressure or make the engine run slightly richer. So in the case of your Audi, it probably just keeps the boost lower. Problem is that some cars detect low octane fuel with a knock sensor, so knock has to be detected first and then it knows.. but knock at any time is bad for your motor. I know they do have octane sensors for the gas now but who knows... I wouldn't chance it, esp since I'm running a NS Power module and am loving the increase in HP.
Lastly, what car does the OP have? The Ultra A4 can probably survive much better on low octane fuel than the Quattro.
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