My question just applies to the base coopers. FI cars should always use premium, but: has anyone wondered whether 87 or 89 would actually be better for the base Cooper in the winter? It's not out of frugality, and I realize the car can get by on regular anytime. I was thinking today that it could actually be better though.

I ask thinking about my short cold trips I make. When is regular particularly "dangerous" to use? In the hot, hot months of summer, maybe doing a lot of sitting in traffic where air flow is poor. We run premium to avoid knock/pre-detonation, but it makes me wonder - in the below freezing temps of winter, would it be better to run a fuel that burns a little easier? Especially for short trip guys?

Thoughts? Please read before spamming out an answer.

 

Always run high test gas in your MINI. For me it only gets 92 octane. Both our MCS & Justa.

 

did you read the first post?

 

Well the simple answer is that you don't WANT fuel that burns easier. Even when the engine is cold, it is setup for detonation from the spark plugs with the proper air/fuel mixture. By using lower-octane fuel, the air/fuel mixture may detonate in any given combustion chamber before-hand. Your vehicle knows if there is a lower-grade fuel in the tank, and will adjust engine timing and air/fuel mixture to accommodate, but I would not willingly put in the worse fuel.

You have a fair point to be concerned about repeated, short, cold-temperature drives but my suggestion is to follow a "severe service" or "commercial service" maintenance schedule for your vehicle, and to stick to the recommended fuel grade for your car as gasoline does not care about cold weather.

 

thanks for the input.

won't the cold air of the air/fuel mixture prevent faster detonation? isn't that how meth kits work? make it colder, thus harder to burn, then you can run leaner..

basically we've all got cold air intakes in the winter. i'm wondering if the fuel, when very cold, isn't getting burned off properly, and a faster burning gas may "even" it out.

 

I don't know enough tech stuff on how the fuel burns fast/slow etc, but find it safe to think in my mind that whatever reason Premium fuel is recommended in ours cars it would be for hot and cold temps or they would have a * beside it in the manual stating in cold climates you can use the cheap stuff... Most people want to use higher octane for the performance and cleaning aspects of it.. Granted going from 87 to 91 octane isn't go to provide much of a performance gain..

 

Ambient temp is a pretty minor contributor to detonation and preignition...
The heat caused by the compression Causes issues...the compression ratio of the motor (both physical and combined with "boost") that can cause issues...just read about what " octane " is, but basicly how well a fuel resists self igniting, from the fuel air mixture getting compressed...
Since you car is a cooper (pretty sure gen2 is OK with 87) you are fine ..if the engineers say it OK, its OK...
Sure...the extra volility of lower octane can help starting in extreme cold, but most areas in the country do use seasonal fuel blends (done for both clean air rules and long before that for the seasonal changes needed due to physics ) which have diffent VAPOR PREASURE, aka volility, to help cold weather starting or the reverse, in hot weather, vapor lock...(remember before ethanol was added to fuel, folks added it to fuel in little bottles, as both dry gas to absorb water, and to help fuel evoprate, increasing thecvapor pressure to make starts easier).
So to answer you question...if your car is OK by the engineers to run 87, I doubt you will see much of a difference, but I bet you will get an extra 5hp or do from the extra timing with 89+ fuel as " recommended " by Mini....

 

true, but 30deg is a lot different from 100deg and sitting in hot traffic, which is what 93 has to be ready for.

I believe the manual says you can run 87, but beware increased chance of pre-detonation. Just wondering if the winter air negates that. Good info on the fuel.

 

Yup...in hot weather you will have less "margin"....
So as the knock sensor, etc senses activity, the computer will reduce timing and enrichen the mixture...
Beck in the carb days, (yes, some cars did have a timing advance , but rare) you had only your right foot and a " choke" to do this...or the motor would blow...
Early computers had some adaptive tricks to prevent issues...
But newer, faster computers, means the motor can USUALLY prevent a major issue unless there is a physical issue...

 

If you are really worried about power, then get to a dyno and measure what happens when you use different grades of fuel. You'll have to drain the tank between each test, of course. Might as well check different brands while you're at it.

Or just run what the manual says. I think the manual for my 2012 Justa specifies at least 87, but recommends 89 or better.

Or, if it makes you feel better, run the highest octane rating non-race non-av gas you can find. That's what I wind up doing, running California's finest 91-octane fuel. I just feel better about it, and I'm not going to stress on the 10 cents per gallon difference between mid-grade and super.

That said, I've run 87 once accidentally (basically a full tank) and noticed no adverse effects.

 

You can get away with the lower octane in the winter but it isn't going to be "better". If you are relying on the fuel to be easy to ignite, you need a better ignition system A drop in intake air temp is similar to an increase in octane but you can't really "over octane" an engine in practice. You could run super high octane race gas in the winter and it should be just fine, until it coats everything with lead I have an MCS, and I noticed a significant drop in fuel economy when I ran a tank of regular through it (just on a long trip, lazy highway miles, not much load). I assume (pretty certain) that this was due to the car retarding the ignition timing to fight detonation. Retarded timing can be hard on an engine as well, it increases EGT's. If you want to run regular in the winter, and don't see a significant drop in fuel economy, I don't see any real reason not to (assuming the car says it is OK, which I think it does), but it won't be "better" other than possibly on your wallet. How heavily loaded the engine is makes a huge difference in octane requirements as well. A higher load (torque, not necessarily power, low RPM's are usually worse for detonation) packs more air into the cylinder, raising your EFFECTIVE compression ratio, the actual pressure in the cylinder at the end of the compression stroke. This is actually one of the main reasons you get better fuel economy in a higher gear Hopefully that all makes sense...

 

Any good Speed Shop that sells racing fuel will also have unleaded racing fuel. Anywhere from 100 octane to 110 or so...

 

Not needed. And if you go too far, you may encounter problems, at least judging by anecdotal evidence. Specifically:

A number of years ago, 80-octane AvGas (aviation gasoline) was phased out. The approved way to run engines that required it was to pay a bunch of $$$ to get re-certified for 87-ocante MoGas (motor vehicle gasoline). Some people didn't want to pay, and they just started putting 110-octane AvGas in. After a few months, their motors started failing with burned exhaust valves.

The FAA investigation, which my grandfather was involved in, concluded that the high-octane fuel was still burning as it went past the exhaust valve into the manifold, overheating and burning the valve. Lots of planes were grounded for that...

That said, aviation engines are vastly different than our engines. Engine management in an aviation engine is utterly primitive compared to the modern systems we have. And you're very unlikely to be able to find fuel that is a full 30 points higher octane rating than is called for in our engines. (That'd be about 120 octane!)

But there may be some small risk--and you're paying something like double the price for race gas than for premium unleaded, for basically no benefit.

 

+1
Worked for a FBO (as a flight instructor, ocassioal fueler)and the company had BURNT THE valves out of a gasoline powered fuel truck running on 100 octane aviation fuel...so we had to add a half quart of motor oil to the trucks fuel tank to drop the octane if we had to fill up the trucks gas tank with 100 octane if the untaxed 89 octane roadfuel storage tank was empty once the truck was fixed......

 

Yup - there is definitely such a thing as too high octane.

I tried posting this on another forum, the basic gist of that was that actually the best time to run 89 is for those long highway drives - light throttle, low load etc.

Otherwise, cold air has relatively low impact on knock resistance. That said, the likelihood of our cars to knock in general on 89 is probably fairly low in normal driving scenarios.

For evos we have something called evoscan where I can datalog and see stuff like counts of knock, throttle, air temp, air fuel ratio, boost, etc. does anyone who tunes minis have anything like that? even on stock maps cars will get a few counts of knock when racing

 

There is no such thing as too much octane (assuming you are still using some form of gasoline) but there is such as thing as too slow of burning fuel. The two can be related, but they don't necessarily need to be. Race fuels tend to burn fast, because they are used in high RPM engines, AvGas tends to burn slow, because it is used in low RPM engines.
http://www.racegas.com/article/38
http://www.racegas.com/article/10
Please note that I did find an article on VP's website but the condition they are describing sounds like a misfire and wrong burn speed, not necessarily octane. If you can't get a high octane fuel to burn, you need a stronger ignition. You could argue that you are "over octaning" said engine, but I would argue that you are "under ignitioning (or something...)" the engine. All of this is really rubbish, since the OP was asking about using 87 or 89 octane in the winter. You want to burn a valve? Retard your timing several degrees and leave it there, your EGT's will go nuts A slow burning fuel, like Avgas, will do the same thing.

 

i thought it only retards timing AFTER the knock sensor senses knock?

 

If you're going to run low octane fuel, I'd make sure the knock sensor is working properly, and I'm not sure how you check that (except hook it up to a scope and
tap on it with a screwdriver or wrench).

 

Kyoo, that is correct. If it detects knock, it will retard the timing and hold it there for a little while then try to add it back, then retard it once it gets knock again and just keep repeating. If you use lower octane fuel you are more likely to get knock and therefore more likely to have retarded timing. Kind of like the oxygen sensor trims fuel but I'm not sure if the computer learns the ignition advance curve or if it keeps trying to default to the base.

 

Man you all make this way more complicated than it need to be.


In a Justa, run the 87. If the engine management system detects that there is so much detonation that it can't control it, you will get a check engine light. (I really doubt that will happen with 87...) But if it does, use 89...

 

the problem is that when the detonation happens and timing is pulled back, the damage is already done. anyway, i will give 89 a shot the next fill up i have, thanks all

 

It really depends. I seriously doubt a justa is going to hurt itself on 87...

 

One data point: I ran a tank full of "California's finest" 87 in my Justa by accident earlier this year. No issues that I could determine--not even any MPG lost!

That said, I'm not exactly eager to repeat the experiment. Fenimore has always gotten 91, except for that tank and possibly the original factory fill.

 

LIGHT detonation isn't terrible. It's not good but it isn't going to ruin your engine immediately. If you use lower octane fuel, just take it easy, especially at first. BUT if MINI says you can run 87, it will make it work even if you give it a decent flogging. MINI isn't going to say a fuel is OK to use if it is going to risk immediate catastrophic engine failure. If I had a Justa, I wouldn't hesitate to try 87, my MCS lost enough MPG to pretty much cancel the extra cost of 93 AND if it is losing that much MPG, it must be retarding the timing a fair amount, which, long term, isn't going to be good for lots of things. If your MPG stays the same, then it shouldn't be retarding the timing significantly. I stand by my earlier statement of it wont be BETTER (for the engine), but probably cheaper.

Richardsperry is very correct, we are making this too complicated

 

Straight from Owner's Manual for R57 Convertible:

"Gasoline quality
The manufacturer of your MINI recommends:
▷ AKI 91.
▷ John Cooper Works AKI 93.
Minimum fuel grade
The manufacturer of your MINI recommends
AKI 89."