In Atlanta you can not get 91 gas only 93. Does gas mix? In other words would a fill of half 93 and half 89 give you 91? At current prices it does not matter as much but once we are back to 4+ it could.

 

I usually just get 93. It's easier and, in spite of people's curious fascination w/ the smallest variations in the price of gas, the difference really isn't huge on a tank. That's what I do anyway....I also only use top tier. I'll cut out other things if necessary, but I want to feed my MINI the good stuff.

 

Yes, mixing gas will create an average octane level.

There are many states where premium can not be found above 91 octane. Consequently Mini has tuned the engine to operate most efficiently at that level. Anecdotally some people on this board feel performance is better with 93, when it is available.

 

+1, Shell 93!

 

If anyone is confused as to what gokartride is talking about, top tier refers to retailers who put additives that really do clean crud out of your engine. This is the site:
http://www.toptiergas.com/retailers.html
I use QuikTrip or Texaco in my state. Oddly, I can't find 91.

 

Funny that Sunoco Canada is on but not the US Sunoco?

 

"Top Tier" actually refers to gasoline brands that participate in the Top Tier gasoline marketing program. There is no empirical evidence that the gasoline being sold by the Top Tier participating brands is any better or worse than the gasoline sold by brands that do not participate. Many major brands do not. The Top Tier marketing program sets specific gasoline formulation requirements, and the participating brands meet those requirements.

 

Just an FYI, lower octane gas has more potential energy per gal than higher octane. So, if you car will run without detonation, lower octane gas will run better. If Mini designed the engine to run on 91 octane it does not help to run 93 octane.

In the old days you could tell if you needed higher octane because of 'pinging'. Now days the engines are equipped with knock sensors that retard the spark before you can tell what is going on.

charlie

 

I prefer to use liquid schwartz whenever possible.

 

On lower octane gasoline your MINI will have less power, not more power, because of the adjustments made by the "anti-knock" sensors. MINI recommends higher octane because it's a higher compression engine. Higher compression means more power per stroke.

 

Except for the numbers you agree with me.

Use the octane gas recommended by the mfg. If they recommend 91 then using 93 will get you less power and mileage, not more.

If you choose to use 89 octane when 91 is recommended then you are correct, it will detonate and the computer will retard the timing, reducing power.

I thought I remembered my manual saying 91 octane (Clubbie S). So that's what I use.

charlie

FWIW, I like having less octane requirement. My WRX needed 93 (or even 94 after mods) and it was sometimes not available. So, I would carry a bottle of octane booster in the trunk.

 

MINI optimized 91 octane because that is cheap gas in Europe. I believe they have 91, 93, 95 IIRC. They didn't create some magic formula and decide that 91 octane was just the best for the engine. There are other countries in the world besides us you know, and 91 is cheap gas for them.

 

91 octane in the U.S. is not equivalent to 91 in Europe. There are two measurement methods for octane levels, "Research" and "Motor". U.S. refiners use an average of the two. European refiners list only the higher "Research" number.

Here is part of the Wikipedia entry on Octane rating:

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.

There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the "headline" octane rating, shown on the pump, is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, the octane shown in the United States is 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, is 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and some even deliver 98 (RON) or 100 (RON).

 

I'm not sure if that's true, or if the engine management software can also adjust to maximize the use of a higher octane gasoline, as well as a lower octane gasoline. I'm not saying you're wrong, I just don't know if the 91 octane recommendation is the "optimal", or "minimum" recommendation.
If the engine can adjust to use the potential of 93 or higher, then you would get more power, and mileage would not suffer.

 

If the car is designed for 91 octane then the cam and compression (and boost in the S) are set up around that octane level. So it will not detonate (under most driving conditions) using 91 octane fuel. If the engine ran better on 93 octane then that's what they would specify. Remember that the EPA mileage numbers are set using the recommended grade of gas so the engine is most efficient with the recommended fuel.

The car can run on 89 octane (and probably even less). You just won't get optimum performance from it.

There can be some extenuating circumstances that modify the issue. Very hot motors, like when in endurance racing or very long and steep hills on very hot days (well over 100deg), can create a need for higher octane levels, but, in 99.99% of driving you'll never see those. Most of those kinds of issues went away (or were greatly reduced) with the improved cooling systems in cars today along with improved alloys.

charlie

 

Just to jump in here and say why not use 87 like i do.

I have run my car for 6 tanks on 91 (highest we can get near me in Mass) and averaged 33.4 mpg. BTW all from the same station.

Then i ran three tanks of 87 as close to empty as i dared (put in over 13 gallons each time) the started the test of 6 tanks and ran an average of 34.8 MPG

Same back and forth driving to work on all tanks, no extended trips out of or in state.

Not only is the 87 cheaper it gets you better gas mileage.

I did the same test in my 03 BMW 525it and with the same results of better mileage with the lower octane gas

and BTW the same in my old 99 dodge pickup

Now this is just my experience but i ma sure many many many other people will find the same, if they really tried it.

 

I must say that I have tracked 4 tanks 2 at 89 and 2 at 93 using the same top tier brand for each tank. With pretty much all city driving with avg speeds of 27 to 31 I get the same 30 hand calculated and 32 from the computer. As for performance I don't see any real difference but I must say I am normall trying to see how good of milage I can get. I wonder how much of the improvment from 91+ would show up in real test like a dyno or 0-60 times. If the regular will not hurt or void any thing I will give it a try.