Pull? You drive a base MINI cooper; no base MINI has a whole lot of pull to begin with. I've been driving a base, no-pull MINI cooper for a year now and, regardless, still love every minute of it. Of course mine has even less pull being that it has a CVT.

 

Well, if you had read it carefully, it said 'not _as much_ pull.' That means that there is less pull than there was before, regardless of one's evaluation of it before the octane change. No, it is certainly no locomotive under the best conditions, but it is worse now with the regular fuel than it was with super.

 

Well, if you had read it carefully, it said 'not _as much_ pull.' That means that there is less pull than there was before, regardless of one's evaluation of it before the octane change. No, it is certainly no locomotive under the best conditions, but it is worse now with the regular fuel than it was with super.

 

NOT TRUE. At first I disagreed with El Jefe but he is correct. A SC or Turbo car can used more octane ... more power.

a normally aspirate engine will not. It would be a waste of money.

You should always use the highest octane gas you can in your MINI or ... your not using its fullest potential ... which is fine if you settle for less HP

 

if ya got a new Mini, you will benefit from higher octane up to points beyond what is available from most street pumps, even without mods....

Thanks for the tales from driving the Cooper, I haven't data logged one. True, it's not boosted, but it has higher compression.....

Matt

 

Sorry, but even normally aspirated engines will benefit from a higher octane level. You should ask owners of M3s in California (and other 91-octane Premium challenged areas) if they have experienced performance gains after switching to 100 octane racing unleaded (or blending the 100 octane stuff to get a higher blended octane level). Personally, my C5 Corvette (with a fairly comprehensive (but not extreme - no s/c) set of mods) runs best on 94-95 octane in summer and 93-94 in winter. If someone wants to ruin their driving experience by saving approximately $2.60-ish each fill-up, that is their business; but advocating that others should run 87 octane in the MINI is a bit of a stretch. The MINI is normally not purchased for its fuel economy. It is nice to be able to have the fun that the MINI provides at a relatively lower operating cost; but don't buy the MINI for an absolute lowest cost to operate - there are too many other cars that cost less than the MINI to operate (but they are nowhere near as fun to drive as the MINI).

 

These two statements of yours seem to contradict themselves. The first one is simply not true. I just went through the 87 test myself and the car does not run as well on it.

The second statement is what I have just proven to myself.

 

Camini ... when I wrote that its was from what I read in most every place that discussed octane myths ... such as The Premium Myth

If your car doesn't knock or ping on lower octane gasoline, paying for higher octane is a waste of your money.

Last night I found interesting info to the contrary. I dont know what the manual says for M3s. Maybe it says to use 93 octane and you can't get it in CA. What about the C5, what does the manual say to use? We can get 93 octane on the East Coast. Anyway, I found out that in the 269HP V6 Rav4s, the manual says to use regular gas "minimum". It turns out that to save on the cost of gas, they are purposely retarding the timing, or whatever its called, and the engine gets less HP. If, in fact, you want the full 269 HP, you use premium. I find that a bit strange that Toyota would do such a thing but I guess every penny counts. This says they are purposely telling consumers to use regular gas but only infer about the lower HP.

I should have said MCS. While Dr O thinks the higher compression MC can use a bit more octane, its certainly true for the MCS. Dr. O "may" be correct depending upon whether or not MINI designed it to run without knocking at a certain octane level. If that is 87 octane then thats the number. If its 91 octane, then thats the number. The point is, whatever the number, going over that number will NOT do anything for a NA engine. On the otherhand, it probably will for a supercharged on Turbo engine.

 

Too many pages to read and not sure if this has been asked.

My understanding is that the higher the compression ratio the higher the octane needed.

Why is it that the MINI has a higher compression ratio than the MINI-S and would that mean it needs a higher octane than the MINI-S?

I guess it is possible the specs I looked at are backwards but still curious none the less.

 

Static compression ratio is not the whole story when it comes to octane requirements - dynamic cylinder pressure is what really determines octane requirements. The supercharger in the 'S' engine greatly increases cylinder pressure, which is why MINI uses a lower static compression ratio to begin with.
Other things affect octane requirements as well. Engines with aluminum cylinder heads can generally get away with higher cylinder pressures than engine with iron heads, for a given fuel octane rating. Valve overlap also affects cylinder pressure, and is determined by the camshaft grind.

In short, static compression ratio is not the final word in octane requirements. I could build a 12.7:1 engine that would run just fine all day on 89 octane gas, given that I made the right choices when it comes to the entire engine.

Scott

 

The higher the cylender pressures and temps the higher the octane needed. You can raise these two by increasing compression, or boosting the motor (like the S with it's supercharger). So while the static compression is lower in the S, the 10 PSI boost (stock) really stuffs more charge into the combustion chamber. Hence the lower static compression.

So, while compression can be used as a good guide for octane requirements, you can't really compare a forced induction compression with a normally asperated compression and have any idea of relative octane requirements.

Hope this helps...

Matt

 

So is the compression ratio speced for the MINI-S only for the main engine and does not account for the additional compressed heat from the supercharger?

 

Static compression is a physical property of engine geometry. It is the ratio of the cylinder volume (includeing combustion chamber) with the piston at bottom dead center to the combustion chamber volume with the piston at top dead center.

Matt

 

Yep, that's the "static" compression ratio, and only accounts for the difference in cylinder volume between when the piston is at the bottom of its stroke and at the top of its stroke. It doesn't really predict the dynamic cylinder pressure or the octane requirements.

Scott

 

just put the min. 91 octane in. Its the min. for a reason. just follow it.

 

higher altitudes don't need as much octane. Hotter temps do. Humidity is an anti-knock agent too. While in the US we get a RON + MON /2 octane, one measures knock under load, and one while not under load. The spread of these numbers says something about the gas quality as well.....

All this being said, there's more to knock point than just octane and compression ratio.

Also, knock sensor motors are tuned more aggressively, and usually can benefit more from higher octane. Cars without a knock sensor need a new tune to take advantage of the higher octane.

Also, the Mini HP rating is only spec'ed at 70 F or something. IF it's hotter, all bets are off!

I'm not surpised that Toyota is bragging about only needing regular is that a lot of non-performance people see that as a real cost savings. Too bad they don't know that the car will loose gas milage if it's under timing retard.... Ah well, the ins and outs of marketing and sales...

Matt

 

I understand this but my question was based on most articles written that only go by static ratios. I don't remember the exact ratio but the Cooper is something like 10:1 and the Cooper-S is something like 7:1.

If you go by this alone then it was confusing why the S model needed 91 Octane until it was nicely explained that the Super Charger forces extra compression justifying the extra octane.

 

If you want to lose a little horsepower to save a little money, go for it. If it doesn't make the engine knock, then it should be ok for the engine. Just remember that the MINI was designed to get a certain power to weight ratio. When you lower the power, especially in a NA Cooper, you are going to have a more sluggish ride from a lower horsepower engine with the same weight.

If anyone has ever used a fuel system cleaner or octane booster, you will definitely notice the difference in horsepower with the higher octane fuel.

 

Actually the MINI (we don't say base here) shows it's power in the lower (read <3k rpm) end. Off the line it will even smoke an "S"...but only for a few seconds. Perhaps it's the CVT that is making you feel thus, but the MINI moves. The "S" moves even better.

 

You missed my point. I said that there isn't a need for >91 fuel. Sure, it'll make your car faster, but you don't need it. The MINI and the "S" will both be fine on 91.

 

when it comes to needs, well, that's pretty subjective. If racing to win is something you do, the faster sure is needed! If one takes your implied definition of what need is, I think we'd all be driving 20 year old toyotas!

I try to stay away from statements like need, and keep with a fact based approach. And it's true that an S floored running 91 will pull timing. I'll let each person evaluate how that impacts their needs....

Matt

 

On UK cars Mini recommed a minimum of 95 Octane. This is probably because this is regular type fuel here. The actual recommended fuel fro my R56 MCS is 97 or higher (our version of premium).

 

The MINI does require/NEED fuel of no less than 91 octane. Some drivers may want to use 93 or greater, and that's fine. Regardless, the MINI doesn't require using >93 for average daily use.

 

but what it comes down to is the ECU is very versetile. It will pull timing, add fuel, whatever, as needed based on temps and knock sensor readings. So the car will run on a huge range of fuels. The crappier the fuel, the more timing is pulled, the less power is generated, and the worse the efficiency gets. There isn't a "hard wall" that I'm aware of where the car just won't run.

You really should get a way from needs, and you're implication that your definition of 'average daily use' is universal just isn't true. Stick to the data, and leave the subjective interpretation to the subjects.

Or are you saying that if you run 89, the car will stop or blow up. Because neither is the truth.

As far as octane ratings go, watch the country you refere to. US and European scales are different. Also, in CA (a whole 1/8th of our population here in the US) 91 is the top grade, other than race fuel and a couple stations that sell 100.

Now I'm sure that I sound like a crotchety fart. That's OK. But I got my information from data logging what the car actually does, not what the manual says, nor from conventional wisdom.

Matt

 

For a supercharged MINI, I guess if you wanted maximum performance and fuel economy under the widest range of driving conditions without breaking the bank, the solution would be to install an auxiliary gas tank filled with higher-octane gas, along with a boost-activated switch so that the engine gets the high-octane stuff once boost rises to the point where the ECU would start pulling timing with the gas in the primary tank.

I guess if you wanted to get fancy, you could even monitor the knock-sensor voltage automatically and have the auxiliary fuel supply cut in when the ECU starts pulling timing. Or the ultimate setup would be an "adaptive fuel system", where a computer-controlled variable valve could be fed by two fuel tanks, one filled with 87 octane and the other filled with 100 octane (or whatever the highest-octane unleaded fuel is that you can find in your area). By having the valve vary the proportions of the two fuels, you could essentially feed the engine 87 octane or 100 octane, or anything in between - whatever the minimum octane would be that would keep the engine from knocking under your current driving conditions.

I don't know how the ECU decides to *stop* retarding the timing, though. Does it wait for a set period of time before attempting to bring the timing back to normal, or are you stuck with the retarded timing until you shut the car off, or until the engine RPMs drop below a certain point?