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My 2018 Q7 3.0 93 vs 87 octane test...

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Old 09-09-2017, 02:55 PM
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Default My 2018 Q7 3.0 93 vs 87 octane test...

The car will potentially retard ignition with 87 octane, and that means less efficient burning, and lower fuel economy.

One post I read said that the lost economy would eat up any savings in fuel purchase. I never believed that for even a second, as premium is 60 cents per gallon more normally where I live. I decided to test it.

They don't sell 91 here, so it is 87, 89, or 93.

My first tank of 93 octane I got 17.69 mpg.

My second tank of 93 octane I got 17.95 mpg.

My third tank, I used 87 octane, and got 18.45 mpg.

Cost savings, at least at prices for the week before the tropical cyclones, was $12 per tankful.
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Old 09-09-2017, 04:23 PM
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Was that your "actual" first tank of gas ever? You might want to rerun these comparisons after you break in the engine a bit... maybe 1000 miles or more?
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Old 09-09-2017, 04:38 PM
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The car came with some gasoline when I bought it. The first tank in the test was my first tank I filled.

I just filled with 87 again. After that, I will go back to a 93 and see if this is a repeating pattern. There is no way to know if my driving was the same, so many tests are needed. In any case, regardless of the exact differences, it is looking very unlikely that 87 has less MPG than 93.

I am at about 950 miles now. Breaking in the car may change the MPG, but I don't see it changing the relative difference or suddenly make 93 have significantly better MPG than 87. My goal was to see if 87 would get 20% less MPG than 93. I didn't think it would, and now I am certain enough that MPG is not a reason to use premium gas.

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Old 09-09-2017, 05:39 PM
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Good for you, you got better mileage. I would never put 87 in a new car that recommends 91
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Old 09-09-2017, 08:30 PM
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I may be mistaken but I thought it was pretty standard fare that 87 will usually net better fuel economy at the expense of power. It has been discussed before.
As others have said, not something I would do, but I'm sure there are many people who do..including any dealerships entire fleet of loaners.

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Old 09-09-2017, 09:48 PM
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Probably the better MPG is just related to the specific driving for that tankful.
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Old 09-09-2017, 09:52 PM
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Originally Posted by gk1 View Post
I may be mistaken but I thought it was pretty standard fare that 87 will usually net better fuel economy at the expense of power. It has been discussed before.
As others have said, not something I would do, but I'm sure there are many people who do..including any dealerships entire fleet of loaners.
Why would you "never use 87"? Are you suggesting that it somehow is damaging to the engine? That's just silly-talk.... Premium fuel is used to create more horsepower, and the car's ECU (at the manufacturer's choice) is optimized for 91. That doesn't mean 87 is detrimental to use, it just means that you won't achieve the advertised horsepower. Ahhhh...but how much less?!? That's the mythical question most manufacturers will never tell you. (You'll not Ford is the only manufacturer putting in print the difference on some EcoBoost motors, which is rather enlightening when you see the differences) Is it 5 hp less (because you sure will never notice that in the real-world driving) or is it 25 hp less? Since ever engine is tuned differently the difference between power and fuel economy when using 87 versus 91 is always different. However, as this poster is alluding to, in Q7 tune it appears fuel economy is not a beneficial part of the 91 octane tuning, power is the name of the game. Every car is different on how it reacts to different octanes, but don't fall prey to thinking you must use 91 in order to maintain your engine properly, because that's just a wise-tale.
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Old 09-10-2017, 04:09 AM
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There was a four peak-HP drop on a GTI when dyno tested.
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Old 09-10-2017, 05:48 AM
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Why does everyone think that somehow octane rating is equivalent to more powerful gasoline? Octane rating has nothing to do with how much power can be produced. Higher octane gasoline is the same as 87 with an exception of additional additives to make it less ignitable hence higher octane rating. All of this is related to how the engines are constructed - compression ratios, forced induction and spark advance. Power extracted from fuel is equivalent to how much of it you can fit in enclosed space and how hard you can compress it before it explodes on it's own. 87 explodes a lot easier at lower compression ratios, higher octane can withstand higher compression ratios and that's how you can 'extract' more power. But unless your engine can run with higher compression, you are not getting more power from just simply putting 91 or 93 in the engine that produces max power with 87, it's just that simple.
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Old 09-11-2017, 07:07 AM
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I laugh when someone thinks that filling 87 will "damage the engine". Please.

Optimal performance with recommended octane rating, but 87 will run just fine for everyday use. It's a mental thing, just like how they sell that "in between" grade for those vehicles that require 87. Oh, let me go a step up to get slightly better quality.

This is why Costco only sells two grades of fuel.

I do not believe that just because invest a few more shiny pennies into a vehicle that you should not try to "save money". If you can save by pumping 87 at the tank, then good for you. I would do it, but my wife would not. There is no right or wrong answer. It's just a matter of preference.
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