I put 89 in my MCS by mistake once (I was in an 89 mode - my Triumph Speed Triple, with something like a 12 - 1 CR uses 89) and drove really easy for 1/2 a tank until I could fill up with 93. No problems, but remember, I drove really easy. The money you'd save just isn't worth it.

 

I switched to 89 as soon as gas prices skyrocketed a few months back, and guess what...my MCS'05 runs better! not only does it NOT knock as much, I got rid of the pesky hesitation I was getting on cold starts (in Florida).
Before this move (yes, it is a 20K car) I wrote to mini about this specific change, and this is the answer I got:

Thanks for writing MINI. We appreciate that you want to take care of
your baby.

MINI Division requires the use of premium fuel (91 AKI) only if the
consumer wants to duplicate the official EPA certified emissions and fuel
economy. However, if the consumer chooses to use less then 91 AKI (it
is not recommended to use below 87 AKI), it will not harm the engine.
It is important to note that there will be a reduction in fuel economy
and performance and emissions will increase.

So I think the extreme opinions are a little too extreme, and I for one will go to a nice restaurant with my wife one night and say" this is one is on mi-ni" with the eighty bucks I saved.

 

If you're willing to experience a reduction in fuel economy and performance and (if you're OK with the idea) that emissions will increase... go ahead. How much performance will you lose? How much fuel economy will you lose? I don't know.

If you assume the the reduction in fuel economy reduces your savings in 20,000 miles from $80 to $55, and if you factor in the extra fill up, and if (on that extra gas stop) you buy $5 worth of convenience store junk like candy, gum and soft drinks... you still save $50/year.

Hopefully someone else can help us evaluate the performance reduction. Likewise, I'm not the best person to defend the emissions impact. For me, it's 93 octane at a Top-Tier approved station. Then again, I'm running more than stock boost and I have a heavy right foot.

 

I tried to say all along that if your MINI seemed OK, ie., runs smooth and doesn't knock, it is OK. There's something about the word, "premium" that makes people believe it is a lot more of a step up from regular than it actually is.

I bet you don't see any difference in gas mileage either.

Enjoy the restaurant.

 

This makes absolutely no sense to me. I'm not saying its not 100% true, but I'm scratching my head. As I understand things and I'm no expert, the higher the octane, the more resistant to pre-detonation the fuel is. AFAIK, knock (dieseling) occurs as a result of the mixture being ignited prematurely, prior to the spark plug firing. How on earth can lowering the octane help, unless whats happening is the ECU is detecting knock and retarding and/or lowering boost pressure more severely to eliminate it. In which case I woud have thought the drop in performance would be noticable. So can someone explain to me what I'm missing, where I've got this wrong or how lower octane could possibly help?

 

OK I just read the 4+ pages, dating back to Summer 2005, and found no reason to change my expensive fuel-buying habit (*SIGH).

If asked, my advice would be to get the right gas (something ELSE might break, right?)

Can't we do better than that?
Tatt

 

I figure with the SC you need the higher grade gas. 91 should be more than enough. Don't really see the need to put in 93. Of course I am sure I will get a few gallons of 100 octane and plop it in

 

Icubed,

Premium gasoline has more energy that regular gasoline, the additives just bring this down a bit so both grades have nearly the same.

Specific Calorific Value MJ/kg for regular gas is 42.7; premium is 43.5. Granted, premium runs a little densor (0.730 to 0.780 l/kg vs. 0.715 to 0.765 for regular, but at the pre-additive stage premium holds the slight edge.

I agree with your other points.

Sincerely,
RockC.

 

As the spark triggered flame front advances through the combustion chamber the unburned fuel/air mixture increases in heat from radiated heat and increasing pressure.

A higher octane gasoline is less prone to breaking down into pre-ignitable compounds ahead of the spark plug triggered flame front in this increasing temperature environment.

In the case of an engine designed to use high octane gasoline that is fed a lower octane gasoline and the driver reports the engine runs better, the report has to be suspect.

Doesn't mean the driver is lying, but the reason for the improvement in the engine's performance can come not from the lower octane rating but from a much fresher batch of gasoline. Besides fresher, the new fill up can be a more recent blend of gasoline that is blended for the current weather conditions which can make an engine perk up some as some off the line stumbling can disappear.

Also, with modern cars, how you drive the car can impact engine performance. Driving the car back and forth the grocery store then taking the car out for a mountain road thrash will find the car a bit flat at first, until the engine controller relearns some things about the engine's requirements and puts these into play.

Finally there are differences between brands of gasoline -- mainly in the additive package -- and some cars perform a bit better (or worse) depending upon the gasoline brand.

A good idea, if you're really wanting to get the most from your car, is to experiment with different brands of gasoline until you find one that your car seems to like, then stay with it as much as possible. However, depending upon how much business the station does, you can still on occasion fill up with "old" gasoline and you might find your car having an off "tank".

Sincerely,

RockC.

 

I have been following this thread and have a similar question about fuel. There is no doubt in my mind about minimum octane. My question is, does anyone have any preferences to brands. I can tell you, although I have no data to back it up, that my previous cars ran differently depending on the brand. My Honda Accord loved Amoco....nothing else. My Jeep loved Sunoco....nothing else. I could 'feel' the differences in brands...regardless what anyone else says about all gas being the same. Those two vehicles just ran smoother and responded better on those brands.

I've seen the post on Top Tier dealers as far as detergents go. My only problem with that is that those dealers are virtually non-existent in Southeast PA. Shell and Texaco are in these parts, but I gotta drive almost 20 miles to get to one of those stations. Sunoco's are plentiful, but they don't show up on the Top Tier list. My dealer claims that Sunoco has the detergent package I'm looking for with the 93.

But once again....does anyone notice any performance differences from one brand to another.....at the same octane level? What gas does the MCS 'seem' to be most fond of.....all engineering mumbo jumbo aside.

 

Here is some real world testing.Just did a trip to florida and back .Thought I would see at steady speed what difference it would make.Did 4 fills on way down.2 fills with 89 oct 2 with 93 oct.Mi /tank fill 1-362 mi fill 2-372 mi fill 3-381 mi fill4-402.Steady at 65-70 mph.Avg including stops 55.3 mph.Didnt bother to change on way back.Some observation:as soon as we got on fill 4 the yo yo reappeared.This has been gone since nov 05(winter gas)As you notice not a great deal of economy difference at steady speed.The computer makes some changes to adjust for lower octane but I think as theory goes it just adjusts to stop knock.We run 15% pulley and cai with cold plugs.The only difference I noticed was slight change in engine sound. I,m sure it might effect acceleration but it has very little affect at highway speed.

 

Interesting test, but quick someone hide this post from the warranty police .

 

I think you have this wrong. Lower octanes have more BTU energy than the higher octanes is what I have always read. The higher compression motors are more prone to the detonation so they need the higher "knock" index, but there is actually LESS "energy" in the higher octane fuels. So everyone who thinks premium is giving their cars more energy has always been wrong...

 

right

 

Are you sure? I thought that lower octane means easier to ignite by compression not higher BTU content.


http://auto.howstuffworks.com/question90.htm



Paul

 

Yo Right

 

From what I have been able to find, it's the higher compression motors that are what gives us the higher HP. Those motors may be more susceptible to "knock" so you you might need more "anti-knock", i.e. octane. But not so much as when we all ran carbs instead of FI. The best gasoline seems to be the lowest octane your car can run without any pinging. Consistency in batches of gasoline seems to be the biggest variable, but right now it seems all the stations are still drawing their gasolines from the same refinery pipeline. Some brands, Chevron comes to mind, have a better additive package, but every gas retailer is sucking from the same refinery tube as far as batches of consistent gas are concerned. So every tank probably is a crap shoot. Could be the batches are more consistent with the premiums because they take more energy to make them, but that is a guess, I don't know that for sure. But yes I have also read that lower octanes contain more BTUs. All tuners agree that just using a higher octane gas will do nothing to increase the power of the motor and may actually reduce the power, without more.http://ttp://www.baltimoresun.com/business/bal-te.md.premium25aug25,1,9362.story?page=1&coll=bal-business-indepth

 

CDMINI,

Lower octane gas has more energy (BTUs) that higher octane gas?

Not according to Bosch and its Automotive Handbook. In fact, premium octane gas has a bit more energy than regular gasoline.

Other sources indicate there is no significant difference in energy content between the various grades of gasoline.

The primary difference between the grades of gasoline is octane rating and if the engine is designed to use a premium grade of gasoline it will derive more useful work from burning that gasoline than a regular grade while subjecting the combustion chamber downstream engine components to a lower exhaust gas temperature.

Therefore, using premium grade gasoline in an engine designed for it, as is the case of the MINI, it is a win win situation in my book.

Sincerely,

RockC.

 

See also... and note where he says higher octane fuel may lower performance in a lightly modified motor. That probably is almost everyone here as I doubt if more than a very few have raised the compression ratio of their modded motors.http://www.motorcycle.com/mo/mcnuts/rt-fuel1.html

 

JDJEFF58,

I don't (yet) have a MCS, so I can't respond with any direct experience concerning any preference the MINI might have for one brand of gasoline vs. another.

However, seat of the pants, my Porsche engine feels stronger when I fill up (here in the Livermore CA area) with Chevron 90/91 or Shell 90/91 gasoline vs. other brands.

(My other car is a diesel and so far I've found no differences between the various stations and their diesel fuels. Diesel fuel is diesel fuel, apparently, though fresher is better and fresher implies the fuel is "tuned" for the current ambient temperatures in the area where the fuel is sold.)

Sincerely,

RockC.

 

To maximize power in high compression applications, IE Supercharging/twincharging or just straigh old high compression engines higer octane is needed to prevent detonation BEFORE TDC, That would actually reduce power. Of course too much one way or another would not be optimal. But since we spark ignite I don't see a decrease in power with higher octane. Just a reduction in the weight of wallet. Haven't found any BTU content comparisons to premium vs regular but found this:
http://www.answers.com/topic/petrol

I'd be willingto bet that even if lower octane has more BTU is is less able to be utilized by the engine to make HP(pre detonation) so its a red herring it there but you cant use it.



From your article:


Bottom line, Says in manual to use 93. Difference between full tank regular and premium at .50 a gallon difference in price, $6.50. Cost of a MCS engine or maintenance?

The best gas I use is Shell VPOWER on my ride back and forth to Massachusetts I get better mileage and car feels better.

Preignition is rough on an engine...is it worth $6.50 to gamble a 20K+ car?



Paul

 

Check out the motorcycle tuners article, from it I would say there is little or no consistency in batches of gasoline that we get at the pump. He buys race gas just to have batch consistency not necessarily for performance, plus all the other variables he talks about. What is the compression ratio on our stock MCS's, 8.3 to 1, that isn't exactly a high compression number like on the motorcycles which are 10 to 12 or even 14 to 1 or so. Just an opinion, these things redline at 7K or so, I don't think anyone is going to blow them up or damage them with a lower octane. The motos are revving to 14, 15 and 17K rpm, now that's going to be a high compression motor. That's street stock, not even modified for racetrack. I buy what I want in the tank. I used to swear by Amoco, but then I saw their additive package wasn't even on the list for recommended street fuels. Never seemed to hurt any of my motos and they were revving to 10-12K a lot of the time.

P.S. The straight MC is a higher compression motor than our MCS, it's a 10.6 to 1.

 

YES!.....Now I see I'm not the only one who notices differences between brands. Time will tell with the Mini, I guess.

 

Ummm, not go too off topic, but there are variations in diesel fuel. Some examples (by no means complete): high sulfur vs. Ultra Low Sulfur (<5 ppm of Sulfur), cetane rating varies by refiner (in fact, different states have different minimum cetane specifications for diesel that can be legally sold in the state), biodiesel blends (5% bd, 20% bd, 100% bd), and, and, and. Stating that diesel is diesel is very similar to stating that gasoline is gasoline.

 

Out of curiousity, where in the manual does it say to use 93 octane? In my manual (2005 MCSa), it says on page 94, under the heading Required Fuel, Premium Unleaded Gasoline, Minimum Octane Rating: 91. Has something changed in the way of octane requirements for a stock MCS/MCSa?