My (limited) understanding is that the actual pressure in the chamber is what matters, rather than the ratio. So, the turbo would create a higher chamber pressure. However, 11:1 seems like a pretty high ratio. So, it makes sense that the MC would need 91+ as well.

 

I have a turbo and since I bought the car I have used only BP 93 octane. However, when the temp. dips below 20 degrees, my mini will not keep running. No problem starting, just cuts out after about 15 seconds and then restarts like a charm, only to cut out 15 seconds later (if that long). When I picked up my car, the dealer said that she mixes every other tank 89/91 and has had no problems in hers. Then my dad (who lives in the snow belt) informed me that in cold weather you don't need the higher octane. So, during the frigid past week, I tried 89 octane and had no stalling problems below 20 degrees whatsoever! Also, on my travels around the country, I have noticed that in higher latitude regions, the octane of gas being sold from the station is lower than what I'm used to. Seems latitude has an effect on the octane of gas, so why not the air temperature??? I'm using 89 for now, but will switch back to 93 when the temp. warms.

 

In the province of British Columbia, I have four choices from a Chevron Gas Station.

87
89
92
94

I go for the 92. Some gas stations will have 90 and a 94. Frustrating at times but now I just fill up at the same station.

 

2006 MCS on a strict diet of 87 AKI = 29-30 mpg
Our new 08 MC will only receive 87 AKI as well
Greg

 

Why?

 

Just don't believe in buying a "higher" quality fuel than truly needed. I know, I know, it's been hotly debated. My frugal (aka cheap) side just won't let me do it.

 

Only the good stuff! For the few cents a gallon or a dollar or two a tank is well worth the difference. Nothing but the best for our MINI's

 

True, it's been almost as debated as "how often should I change my oil?". It does say in the manual that you won't hurt the engine if you use lower than recommended octane gas. I take that as the truth, otherwise there'd be BIG RED LETTERS somewhere on the car. Truthfully, how could they justify making an engine that could be damaged with easily acquiered octane fuels? Can you imagine the number of cars in for warranty covered damage if that were the case? As for me I subscribe to the 91 octane club (highest available in AZ).

 

I run 87 or 93 with no noticeable differences. I record all my milage. My driving routine is too variable to get a good sense of which is better, varies 31 to 37 MPG with either grade. I try to avoid stations that look like crap figuring their gas would too.

If you feel your engine is down on power or self destructing with 87 then run 93. If you feel the 2 bucks in your pocket missing, run the 87. Either way I believe the feeling is going to be more significant to you than the reality.

 

Have you tried checking the mpg with 87 vs. 91+? Might be interesting to see if you really are saving that $2.

 

Greg, a higher quality fuel is not the same thing as a higher octane. Oil companies name the higher octane fuels as premium, but it is a misnomer/marketing gimmick. Octane rating or AKI (AntiKnock Index) has to do with the gasoline's ability to resist ignition, specifically while being compressed. You only want gas to ignite when the spark plug ignites otherwise you get the knocking and pinging due to detonation in the compression chamber. This is the reason that high compression ratio engines such as the Prince in the R56 requires 91 AKI.

The amount of detergent in gasolines is regulated by the EPA and good quality fuel has extra additives that can help prevent buildup. Some gas stations illegally dilute fuel by adding water or other crap which is obviously not good for your car.

My recommendation is to add whatever octane fuel your manual recommends. Just realize that if you put an 87 octane fuel, the ECU will compensate for this so you won't get knocking, but you're not getting something for nothing. Your performance level will be less and possibly mileage depending on temperature. If you want to really save money, I'd suggest putting 89 in the winter months and 91/93 in the summer months.

I would avoid putting in octanes that are higher than the recommended AKI of 91 (only exception is when 91 is not available). Most experts will tell you that you're wasting your money as performance will not improve and the higher octane is usually made by adding more Ethanol to the gas which can hurt mileage. There are even cases where all the fuel will not ignite and can cause damage to components. This is one of the reasons it doesn't say in the manual, use the highest octane possible whenever available. It says to use 91 and use top quality fuel. I've spoken to a couple of experts at MINI about this and was told that the manual recommends 91 AKI as a conservative estimate and that in actuality, the engine runs best with 89 AKI. That being said, I've personally only used 91/93 thus far.

 

I don't have 91 octane available here only 93, except for billy-bob gas.
I have heard others and dealers recommend 89 for colder climates as well and I may try a tank of that next time I fill up. This taken from the mini R56 manual:


Super Premium gasoline/AKI91
This gasoline is highly recommended.
However, you may also use gasoline with less
AKI. The minimum AKI Rating is 87.
If you use gasoline with this minimum AKI Rat-
ing, the engine may produce knocking sounds
when starting at high outside temperatures. This
has no effect on the engine life.
Do not use any gasoline below the speci-
fied minimum fuel grade. Otherwise the
engine could be damaged.<

So it would seem that 87 is acceptable. My MA told me that for normal driving around town in my MC, I'd probably not notice a difference running 87 octane, buy would at highway speeds. Given all that, I've still never put anything in other than Shell 93, if I could get a decent brand at 91, I'd try it, I may try a 89 shell.

 

i use either Shell or Chevron supreme... in Oregon its 92 octane!!

 

Shell 93 for mine.Although I have been known to visit my local Texaco and fill with the 100 octane every so often. That six bucks a gallon price never seems to change. MPG suffers but she's so much more peppy

 

all fuel in the U.S. must meet minimum standards...gas is distilled by a handful of refineries and then the Shells, Chevrons, BPs, etc add their magic (smoke & mirrors).
quality gas is a myth. if you think otherwise stations do sell "racing fuels" and that is what I use and I consistently run red lights so fast that I am not detectable by foto enforcement.

 

This, listen to this.

Consumer reports did a completely independent test http://www.consumerreports.org/car-m...h-extra-price/
which found it really does run cleaner.

so higher octane for the higher effective pressure for turbos, and yes use good gas. If you have a costco near you its a no brainer.

 

For several years I have been mixing 91/93 (10% ethanol) with 90 (0 percent ethanol). My reason is to run some what less than 10 % ethanol at all times. Cost is not part of the equation....ethanol is.

I have noticed that as long as I am running a 'top tier' brand, I am not experiencing degradation in performance. I have always believed the use of ethanol is to blame for many many of our issues.