You are correct the car can not test the octane level, but the knock sensors can detect spark knock and then retard the timing. You will NOT hurt the car useing 87-89 octane.

 

What octane butter? Hmmm. Low-test just doesn't taste the same.

 

There are strong opinions on this forum about whether one should only use 91+ AKI in the Prince engine. I'm of the "Best to stay with 91+ school." The Owner's Manual says that using 87 wont void the warranty, but may cause knocking.

Regarding the issue of whether this affects only the MCS, it should be understood that the MC engine has a higher compression ratio (11.1:1) than the MCS engine (10.5:1). Although the turbo makes for higher pressure, 11:1 is pretty high.

As far as whether 91+ gives better mph than 87, You would need to run several tanks of each to sort that out. There are a number of factors that can cause variation in how much gas fills your tank with a fill up. Ambient temp can affect it. Variations in the pumps, and early shut-off can also throw the results off.

IIRC, altitude can have an effect as well what AKI gas is required. Thinner air, less pressure in the cylinder. However, it would probably only amount to one AKI from sea-level to Denver.

 

Here in Europe we have only 95 or 100 octanes and the difference is very apparent in both mileage and performance

 

And that is???? We are waiting on baited breath

 

Yes but you all measure your octane different over there than we do in the USA....it all works out though.

 

I agree with Robin, and would like to add that if you are doing a highway trip then you willnot notice any knocking with 87/89...but if you are doing a lot of full throttling then you might get some knocking but even then that sometimes depends on the outside temp.

Robin, what do you mean by early shut off?

 

Sorry about that... I found that the 100 octanes was the best one for both mileage and performance...
Thanks mdrums I wasn't aware that they measure octanes differently here in Europe.

 

The gas station pump shuts off before the tank over-flows. I believe there can be some variation in the exact level at which different pumps shut off. So, the 87 pump may have shut off earlier than the 91 pump, or vice versa.

In the USA, the number is actually called the Anti-Knock Index (AKI) and is 4 to 5 points lower than the European number.
http://en.wikipedia.org/wiki/Octane_...ndex_.28AKI.29
Europe uses the Research Octane Number (RON). We use a combination of RON and Motor Octane Number. Since it is a combination of two different octane tests, we call it AKI.

 

Robin, I was unaware due to not researching the MCS as much as the MC when I was doing my shopping that the S is only a 10.5:1, but either way the effect of the turbo packing the air in there should still get us to the same effect on pressure from the ideal gas law as the 11:1 ratio MC. The pressure is what leads to the detonation instead of a nice even burn of the fuel.

Regarding ignition timing. The spark plug goes off before the piston reaches top dead center (TDC) so that the fuel is completly burned at about 12 degrees after TDC (ATDC). If the knock sensor determines that there is indeed knock the timing map determines that the spark plug must go off earlier. This can still lead to detonation at TDC because the goal is to burn the fuel completly at 12 degrees ATDC, especially true at high engine speeds. So if you can manage to never ever take the engine over 3k rpm 87 octane will do ya. But lets be realistic here, wasnt the break in period where we werent supposed to go over 4500RPM the worst 1200 miles of your life. I know I was itching to hear my lil 1.6 ROAR!

 

I get 32 mpg like clockwork. 09 MCS w/ premium gas. 50/50 split of highway and city driving.

 

My 2 cents: (I'm in Canada, so that's 1.6 cents US )

I've used a mix of 87, 91, and Sunoco Ultra94 fuel in my '08 JustaCooper in a series of totally unscientific tests over the past one year + of driving.

In normal, day-to-day commuting, I've never heard any pinging. Never noticed any difference in engine power. No noticeable difference in fuel economy. My MINI doesn't seem to care what octane fuel it drinks.

I always buy gas from a name-brand station. I don't track my MINI. I do like to "flog" it every now and then (I live in a rural area, lots of nice empty country roads to safely explore the 6000 rpm redline and fabulous handling/braking). I've even done the "ping test" a few times with different fuels (the ping test: put it in 3rd gear, low rpm's, drive up a moderately steep hill with the gas pedal floored on a hot day. If it's going to "ping", this will cause it). Nothing.

Now I'm sure that when I'm using 87 octane fuel, the engine management computer retards the timing to avoid knock, so there's less power, etc. My point is, I don't notice it in daily use. The engine doesn't seem to care.

If I had an "S" or a JCW on a track - - Ultra94 for sure. But in my JustaCooper on a daily run-of-the-mill commute? Not necessary, in my experience.

As I said, just my 1.6 cents (US).



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run what you want in your own car but don't be giving out dangerous advice.

 

How is that dangerous advice?

 

You want some dangerous advice? Here's some dangerous advice...

"Go ahead, play in traffic! Nothing will happen."

"You and your brother, play "jousting" with that pointed stick, you can't poke your eye out!"

"That Mister Madoff seems so nice - go ahead and sign over your 401K to him."

Now THAT'S dangerous advice.


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I would like to see all the data that states you will damage your engine by running 87 octane in the MINI (or any other engine designed to run on USA Fuel).

No Person that has ever stated this on these forums has been able to come up with this documentation to show it will damage the engine.

The real fact is that Shell, Mobil, and others have proven otherwise in there testing. Just look it up on their respective websites.

BTW my 08 clubman runs better on 87 than it does on 91 and gives me better gas mileage on the 87 as well.

 

You seem to know a lot about chemistry but your engine mechanics need a smidge of work

Retarding the timing means that it fires closer to TDC or after TDC. The goal there is to reduce cylinder pressure and heat (placing it farther down the exhaust stream) in the cylinder to try and stop the unstable combustion event (which doesn't just happen on one revolution).

You are stuck on compressing the air fuel mixture till it ignites like a diesel engine which could happen, but with the amount of ecu safe guards such as electronic boost control (lower cylinder pressure if needed via less boost which also equals less heat), knock detection, and a continously learning ecu, it is would be nearly impossilbe to have happen constanly on a non modified system. You can run 89 octane in our engines, you will just be robbing yourself of valuable horsepower.

Also some engines are louder than others, but if you are hearing audible knock inside the cabin, you have major issues. Any good knock detection system should hear it at the on-set and go through the steps to prevent it from getting worse. This is why tuners use very sensitive tools and det cans (microphone) to listen for knock assuming that their setup is limited by the fuel that they are running.

 

This has been covered before but I will restate:

• Either Mini engine has a knock sensor system that protects the engine from knock if the Octane is not high enough for the operating conditions
• If knock is detected, the ECU very quckly retards the spark timing from optimal. (Optimal combustion phasing is generally characterized as 50% of the fuel burned at 6 to 10 degrees ATDC) This gets rid of damaging knock (before you can hear it) and reduces the efficiency of the engine (worse gas mileage)
• Retarded ignition timing also raises the exhaust temperature which may tend to overheat the catalyst converter if you keep your foot in the throttle long enough,
• Knock is most likely at high load and hot and dry ambient conditions
• Knock is least likely at low load or in cool humid conditions
• So if you are taking a liesurely jaunt on a cool and/or humid day, you probably will not get any better gas mileage on high Octane

Dave

 

I'm not going to argue with people who say the ECU will retard timing if it detects knock as that is true.

Guess what. It has to KNOCK before it retards it so you are knocking your pistons. When your engine knocks, even for a moment, well, it hammered your piston AND stored a code in the ECU for MINI to see when you bring it in for service although it may not have turned on the check engine light - and may not show up in a store bought code reader either.

Nobody seems to know how many knocks it will take to hurt your engine but you can be sure if you get piston damage and your ecu shows you've been knocking you will be footing the repair bill.


If you are the type of person who modifies your engine and are willing to accept that you may void your warranty in mysterious ways then you'll be running the highest octane to get more power.

If you are like 95% of the people out there who just want a stock car fully covered by warranty, don't take the chance of voiding your warranty just because you listened to a bunch of internet "experts" who say you can run whatever you want to save a couple dollars per tank full. A $5k engine repair will make you feel pretty stupid for saving a couple dollars per tank of gas. The "experts" are not going to pay for your repair bill.


Just look at how many people had to pay for fuel pump repairs because they were using "bad gas".

 

I always use AKI 91 in my MCS.

I've always heard that knocking was hard on the engine. However, MINI seems to disagree. From the 2007 version of the Owners Manual:
If you use a quality brand gas with an AKI of at least 87 and 10% or less ethanol, they can't void the warranty because they've said it is OK.

This is a different issue. The damage was caused by gas with over 10% ethanol, or running the pump dry (it uses the fuel to cool itself). From the manual:

 

This follows the traditional "use premium particularly for turbocharged or supercharged engines" train of thought, which I tend to agree with. Why would an NA engine in particular need premium?

 

I drive the same 50/50 type split with my 09 MC using 89 and get 42 mpg.

Jim

 

I think you'll get better gas mileage at altitude using 91 versus 87. And knocking can't be a good thing for that engine. I know what it says, but think about it (and not too long).;

 

Back in the '60's and '70's many naturally aspirated engines needed premium fuel. All of the high-horsepower muscle car V8's and most of the small high compression imports, too. A 396 c.i. engine in a '69 SS Camaro, for example, would barely run on regular fuel, the knocking would be so bad.

Sunoco used to sell a grade of fuel they called "260" long ago, I don't remember what the octane number of that was but many of the muscle car guys swore by it, they could crank in more timing and make more power without grenading their engines. I used to use it in my MG and Lotus cars, too (the Lotus had an 1100cc engine with 11.5:1 c.r. and hemi combustion chambers - very picky about fuel!).

I still own my '69 MGB with the high-compression 4 cyl. engine. It runs SO much better on premium you wouldn't believe it. Of course, there is no computer monitoring knock and so on in an MG, so all the adjustments have to be done by me. I can retard the timing enough so that it will run on modern regular (87) fuel without knocking, but the engine feels "flat", no power and terrible fuel mileage. Using the highest octane premium I can find, the timing can be advanced significantly - freer revving, loads more power, good mileage. Go too far, though, and it starts to "ping" and run hot and roughly. Run it too long like that and pistons can start to melt.

Back in the "olden days", we used to set the timing with a light, fill up with the highest grade premium we could find and then go out on the road and do the "ping test" I mentioned in a post above. That was the true test. What you wanted to hear was a tiny bit of initial "ping" for a split second at throttle tip-in that went away immediately. That way, you knew that you had the timing right on that knife-edge balance. If you did the test and didn't hear any hint of ping - you probably had it retarded too much. Loud/noticeable/lasting-longer-than-a-split-second pinging: too far advanced.

That same process is going on in the MINI engine (all modern engines, for that matter) all the time. The only difference is that the computer "listens" for pinging to start, and then retards timing bit by bit until it reaches that "knife edge". You don't have to listen and then go back to the shop and crank in a bit more or less timing, the computer does it all for you without you even being aware of it. Turbo, supercharged, naturally aspirated - - it's all the same. Force-fed engines are more sensitive to octane - more heat and pressure increase the chances of ping occurring, and so also increase the demands on fuel octane.

When you think about it, the way engines work hasn't really changed much, has it? The basics are the same, but everything is run by computers and electronics now. Much more refined... but not much different really. Kinda takes a bit of the fun away, if you ask me...


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I never thought it was fun to get out the timing light and loosen the distributor bolt and turn it. I'd rather just put 91 octane gas in it and call it a day