I can really see the difference in gas milage! I drive the same route in the mountains of Colorado everyday. I tried my first tank with Prem. and my second with Reg. Unleaded. There was a significant difference. Almost an average of 5 miles per gallon. Does this seem to be the common conclusion? I've had it now for two and half weeks, and it just gets to be more fun everyday. No complaints

 

Wait, did you get better mileage on premium? or regular?

 

Sorry, that would of helped, I avg. better milage with the Prem.

 

We use mid grade 89 (09 Cooper S automatic) and get 28 in all city driving. This seems about right with EPA estimate, I think?????????

 

I have never put anything but 93 in my Mini so I can't compare. Since it is a forced induction engine and advised by the manufacturer I have never considered running anything less then 91.

 

Oh god don't use anything but premium you will tear the turbo up. If your are not running a high enough octane it will cause the motor to knock which will tear yo **** up!

 

Octane ratings should not effect fuel economy numbers. More octane is needed in higher compression motors or motors with some sort of forced induction system to prevent pre-detonation and knock. The ecu should make up for the difference between the 2 by retarding the timing or even lowering boost, but all you are really doing is saving $.20 a gallon and robbing yourself of horsepower.

 

False economy, my friend. There's a reason the factory says the car needs PREMIUM. The engine will adjust to run the lesser octane if you need to put it in on a temporary basis, but in the long haul picture, your engine will thrive and last longer running PREMIUM. You DO love your Mini, don't you?
Put it this way...if you had a dog you loved, would you feed him that super cheap dog food that eventually ends with a big vet bill? Same deal with your Mini. Next time you fuel up, put in PREMIUM and keep it that way IF you want to see that engine last. And you're also robbing yourself of PERFORMANCE.
BTW, this has been hashed over in multiple strings many times. Look around the forum, search some key words and read. But put the PREMIUM in the MINI S.

 

1st, I have a Mini Cooper not a S, my first tank was avg. of 45.8 it was great. My second tank I switched to reg. I went to 38.4, still good but not the same. My third tank I thought I'll switch back to prem. and viola, I was at 44.2. I drive from Keystone to Winter Park, Co. almost every day. And I have alot of fun with it on the passes, so I'm not really babeing the thing. But I was just wandering if anyone else has noticed this.

 

I agree, SURFBLUE. But I do have a dog I feed cheaper dog food too, that Dog just drive the family nuts.....

 

Okay. The only advantage is saving a few dollars a week by not puttin premium in. You are otherwise robbing yourself of horsepower and possible engine harm. It costs me an extra eight dollars a month. I think that is a small price to pay. If you are that concerned about extra fuel costs, I'm pretty sure you can find a Chevy Aveo somewhere that used regular.

 

Premium is the fuel of choice. Knocking and detonation can cause extreme heat and pressure inside of the cylinders damaging pistons and heads. At level cruise little will happen, but problems arrise when your foot is in the pedal climbing hills.

 

I realize now that I have upset the Mini Gods, and I beg forgiveness, I've seen other threads that mention using reg. unleaded, but never the difference in milage. I will continue to only use Prem. I've heard the voices of reason and agree. From this day forth only Prem. or maybe.....raceing fuel, that might be fun. Remember its not the money I did buy a Mini.

 

Its all a learning process. I've made my share of mistakes, and not done making them yet. See yah in the mountains!

 

I run 93 in my MC - I have tried 87 twice and thought I noticed a difference but yet it's most likely nothing but a placebo.....

 

I put 89 octane most of the time in my non-turbo '07 Mini Cooper, and can't tell any difference between using that fuel grade or 91 octane. It seems to run "rough" when I use 87, though, but that's probably just my imagination.

I've also been averaging 41.5 MPG over the past 40,000 miles of mostly highway driving, so I have no reason to complain!

 

dunno about the Prince engine, but the non-supercharged Tritec mill in the 1st gen Coopers had higher compression ratios so prem was a neccessity. however, the first gen cars sometimes had difficulty starting and idling in cold weather, and putting in mid-grade every now and then helped out hugely (at least with my 05.)

Just run premium.

 

The engine does not have a variable compression ratio, therefore how does the mini "test" the octane rating of the gas? I am fairly certian it cannont.

All octane rating does is determine how much the fuel can be compressed before it ignites, basic thermodynamics. The MINI uses an 11:1 ratio which requires the 91 octane. If you use less it can simply ignite early and you hear a pinging. This can lead to decreased performance. But the energy content of 89 fuel and 93 fuel should be the same. So as long as you are not detonating the fuel early, you should have no decrease in performance.

 

Just to set the record straight, the title of your thread (Prem. vs. Unleaded) is incorrect. Both premium and regular are unleaded...you can't buy leaded any longer in the US. The title should have been "Premium vs. Regular", which is what all the discussion so far has focused on.

 

all right, lets relax I'm origionaly from Texas home of unleaded.

 

The engines have a higher spark timing which requires premium. You could get the computer re-calibrated to run on 87 and it wouldn't harm the engine. Unless you have done that then I wouldn't run the car on 87 at all unless for emergencies only.

 

The reason for the high octane is the high compression ratio. That is determined by how much volume the air/fuel takes up when the piston is at bottom dead center. vs the volume of the air/fuel at top dead center. In thise case 11:1. No amount of recalibration is going to allow you to run without pinging on 87.

 

Tell the gas station owners. At least where I'm from, lots of gas stations (especially the older franchises) have signs advertising the prices of three grades of fuel: "Unleaded" (87), "Midgrade" (89), and "Premium" (91 or 93).

You can in fact still buy leaded gasoline in the US. Your local airport probably has it under the name "100LL" (100 octane, low lead avgas). It will ruin the catalytic converter if you try to run it in a modern car, though.

 

The thing is you will never hear the pinging. The knock sensor on the engine will feel the predetation and retard the timing. This is where you get the decrease in performance.

 

The only way a sensor can be set off is if it happens. Therefore, a knock sensor will only go off if the engine knocks. You will hear that, sounds like whacking the face of the piston with a hammer.

The BMW Valvetronic system, found in our beloved MINI's, allows for variable timing of both the intake and exhausted valves. As well as, variable lift and duration on the intake side of things. A smaller air/fuel mixture is still going to be compressed at an 11:1 ratio. Which for a low octane rating fuel still will have the ability to detonate early, causing pinging.

Now the exhaust valve is not going to open before the cylinder has fired. First because fuel in the catalytic converter can overheat and cause failure. An overheating converter can act as an engine governer as well. Second, opening the valves, which are supposed to be closed during the compression stroke, can lead to engine failure if the piston head damages the valve. MINI, which can be good or bad a warranty service depending on who you talk to here, is not going to want to deal with bent valves.

I think the lesson to learn here is:
I dont want to whack my piston with a hammer , so lets all just use delicous 91 C8H18 rated fuel .