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Old 08-12-2011, 08:27 PM   #1
05graysport
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Regular(87) vs Premium fuel(93) real test numbers

Alright guys, just wanted to pass some interesting information that I concluded after two full gas tanks.

I have a 2005 325i with 80,000k miles, 1000 miles on the newly changed mobil 1 0w40 oil, new air filter, stock 225/45/17 tires with OEM tire pressure gauging pressures.

I used the vehicle solely for my certain commute and my other vehicle for everything else, just to get an actual test. Obviously both tanks dont have exact driving habits to the T, but they are fairly close.

On Regular 87 Octane, the vehicle put out 243.2 miles on 13.70 gallons.

On Premium 93 Octane, the vehicle put out 258.4 miles on 13.81 gallons.

The car as expected performed significantly better with throttle response ONLY, with 93 Premium octane fuel. I do not race, this car is not intended to race and do not leave the car idling for mass periods of time.

I know there have been many debates as to which fuel to use. In my opinion the difference in throttle response was not even the deciding factor, it was the peace of mind that an octane that is 6 points purer is being used, as this high compression engine states it.

As stated here before, no knocking due to the on board ECU retarding the throttle, to prevent it.

The price difference constantly around my area is $0.22 cents higher for Premium, on 16.6 gallons making the cost, $3.65, however never realistically dipping into the fuel reserves, probably closer to $3.00 per fill up.

The mileage calculates to be: 17.75 MPG on pure 87 octane. 18.81 MPG on pure 93 octane. In my experience, 99% accuracy on the fuel level and MPG to my calculations, I got around 15 Miles more with premium. With a current cost of Premium at $3.85 per gallon, I paid $3.07 in "mileage" to get 15 miles more on my tank, making it 100% WORTHWHILE to use premium as it was basically FREE.

As a long time Audi S4 owner, finally giving in to BMW, I would never ever stick the 87 octane gas in the vehicle due to the higher available octane.

Few points to conclude if you made it this far:

If you drive purely city only, premium fuel at $0.22 cents higher than regular will cost you nothing.

If you drive purely city only, premium fuel HIGHER than $0.22 cents than regular will cost you more.

If you drive mixed with highway, or only Highway, you are loosing money with regular, hands down.

Obviously this all only pertains to those who still believe it is worth using regular 87 octane in a high compression ratio engine, but from the tests I did, if you are really cost conscious and dont care much about your vehicle, $0.20-0.25 is about the area where the cost neutralizes.

The fuel used in the vehicle was from Mobil Gas stations, Shell V power seems to yield greater results, but thats another topic.

Hope this helps some people, maybe trolls in determining that it is not cost friendly to use Regular, however those who must choose to still use 87 can now realize it is not only not beneficial for the engine/throttle response, but it does not save you anything!

Good Luck!
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Old 08-12-2011, 08:32 PM   #2
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Good Info.
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Old 08-12-2011, 08:44 PM   #3
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Thats great info. Finally some good data thats says yes premier is better then regular.

Good job
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Old 08-12-2011, 08:45 PM   #4
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Shell premium is all I use anymore, great info thanks.
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Old 08-12-2011, 09:00 PM   #5
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A price per mile value would be nice to see, but a pretty good post.

Another thing is premium isn't "purer" than regular, nor are you listing the actual octane rating. In the US we used Anti-Knock Index or AKI, because fuel isn't made out of just octane and heptane anymore, and all it tells is the resistance and speed of combustion. Premium could could be more or less "pure" and it has no effect on AKI.
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Old 08-12-2011, 09:03 PM   #6
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Quote:
Originally Posted by 05graysport View Post
Hope this helps some people, maybe trolls in determining that it is not cost friendly to use Regular, however those who must choose to still use 87 can now realize it is not only not beneficial for the engine/throttle response, but it does not save you anything!
Exactly!

Aside from better fuel economy or throttle response it's obvious that premium needs to be used. If I'm not mistaken all of our cars are initially tuned to 91 octane. By using something of a lower quality it can increase wear on the engine.

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Originally Posted by mkodama View Post
Another thing is premium isn't "purer" than regular, nor are you listing the actual octane rating. In the US we used Anti-Knock Index or AKI, because fuel isn't made out of just octane and heptane anymore, and all it tells is the resistance and speed of combustion. Premium could could be more or less "pure" and it has no effect on AKI.
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Old 08-12-2011, 09:16 PM   #7
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Excellent post OP

You've prolly didn't pay that much attention to the wording, but as the other poster noted; premium is not "purer".

The higher the octane the less flamable the fuel is.

It's so to allow for higher compression without premature ignition.

---------------------------

More ...

Fuel heats up under compression and if it's not the proper octane level, it will ignite prematurely.

Last edited by Alpha Beta; 08-12-2011 at 09:23 PM.
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Old 08-12-2011, 10:42 PM   #8
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great post. also another reason for using name brand (more specifically Top Tier) gasonline brand is for deposit control.
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Old 08-12-2011, 11:10 PM   #9
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I stand corrected about the Octane definition. I was always under the impression that gas is derived from crude oil and the ratio or amount of octane in the Fuel is 87 for regular and "more purified" 93 meaning it went through another process to take out more carbon deposits, hence what builds up on fuel injectors over time! Also know that jet engines take very high octane 100+ fuel and I attributed that to the purer fuel needed to run such a high performing engine.

Time to do some reading

Good overall discussion, closes some ends for some folks.
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Old 08-12-2011, 11:39 PM   #10
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Wikipedia has a pretty good explanation of the octane rating. For those who don't want to look it up, I'll try to explain it here:

Iso-octane is arbirtrarily assigned an octane rating of 100, and heptane is assigned a rating of 0. To determine the octane rating (at least back in the day), the fuel would be compared to varying mixtures of iso-octane and heptane. The percentage of iso-octane in the mixture that burns in the same manner as the fuel is the number used to assign the octane rating. A fuel that burns in a very controlled manner may be assigned a rating 93, and one that is very explosive might be something like 20. There is some confusion because there are two different standards for octane rating - the research octane number (RON) and motor octane number (MON). The numbers are determined by different procedures between the two standards. European gas stations go by RON, while the US gas stations go by the Anti Knock Index (which is RON and MON averaged together)

The octane rating only concerns the rate of burning; it has nothing to do with the energy content of the fuel, nor does it have anything to do with the purity of a fuel. Ethanol for example only has 70% the energy of normal gasoline, but it has an octane rating of around 110 (it burns slower than iso-octane)
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Old 08-13-2011, 12:01 AM   #11
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However, I heard higher octane gas has more detergent and I remember seeing some pictures comparing 87 octane gas with 91 octane gas from the same gas station. The 91 octane gas has a lighter color and is clearer too.
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Old 08-13-2011, 12:08 AM   #12
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Thats great info. Finally some good data thats says yes premier is better then regular.

Good job
This
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Old 08-13-2011, 12:18 AM   #13
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Summarized in a single post, using gas prices from my area:

regular: (3.81 $/g)/(17.75 m/g) = $0.215 $/mile
premium: (4.03 $/g)/(18.81 m/g) = $0.214 $/mile + better performance
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Old 08-13-2011, 12:25 AM   #14
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However, I heard higher octane gas has more detergent and I remember seeing some pictures comparing 87 octane gas with 91 octane gas from the same gas station. The 91 octane gas has a lighter color and is clearer too.
Detergents and additives will depend on the brand of gasoline. Some choose to put more "good stuff" in the highest octane gasoline, some put the same stuff in all grades, and some just use crap.
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Old 08-13-2011, 12:31 AM   #15
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great info op.
I've been using premium lately and car feels a lot more responsive. I get about 10miles more a full tank than regular also

again great info...
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Old 08-13-2011, 06:40 AM   #16
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Originally Posted by 05graysport View Post
I stand corrected about the Octane definition. I was always under the impression that gas is derived from crude oil and the ratio or amount of octane in the Fuel is 87 for regular and "more purified" 93 meaning it went through another process to take out more carbon deposits, hence what builds up on fuel injectors over time! Also know that jet engines take very high octane 100+ fuel and I attributed that to the purer fuel needed to run such a high performing engine.

Time to do some reading

Good overall discussion, closes some ends for some folks.
Indeed.

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

It's fairly technical, so I suspect 90% of the people who open this link won't read past the first paragraph or two. But, those who read all 4 parts will have a much better understanding of gasoline and "octane" AKI, etc.

There is a lot of meaningless stuff in this thread and misstatements.

An ECU does not retard the throttle to control knock. Usually it retards timing. It can do many things though including running richer, which while burning more fuel, also cools the combustion.

Compression ratio is but one small factor in the need for higher octane. Fuel/air ratio, volumetric efficiency, even the design of the combustion chamber (and more) all play a role.
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Old 08-13-2011, 09:36 AM   #17
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Detergents and additives will depend on the brand of gasoline. Some choose to put more "good stuff" in the highest octane gasoline, some put the same stuff in all grades, and some just use crap.
correct. chevron/texacco puts techron on all of their grades of gasoline (87-93 oct) but Shell only puts Nitrogen in their V-Power (lower grades don't get as much Nitrogen)
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Old 08-13-2011, 09:39 AM   #18
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I filled up with 87 octane, my MPG on the highway did not go past 28mpg. Added fuel injector cleaner(when close to an empty tank), filled up 93 octane,MPG went up to 29.4mpg.

I am sure if I change fuel filter, and spark plugs. I should be acquiring more MPGs. The dirt cheap 87 gas must have clogged it up since I hear on the forums that everyone hits 30+ mpgs
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Old 08-13-2011, 10:41 AM   #19
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I filled up with 87 octane, my MPG on the highway did not go past 28mpg. Added fuel injector cleaner(when close to an empty tank), filled up 93 octane,MPG went up to 29.4mpg.

I am sure if I change fuel filter, and spark plugs. I should be acquiring more MPGs. The dirt cheap 87 gas must have clogged it up since I hear on the forums that everyone hits 30+ mpgs
I barely get 22
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Old 08-13-2011, 10:47 AM   #20
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Good stuff, but doesn't it take a while for the car to sense the different octane gas? I'm saying if it takes more than just one tank to notice it.
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