Yep, don't say I never taught you anything! (but I still think the hockey game we played with it had something to do with it)

 

Dudes, using lower octane in an engine designed for a higher octane will leave too much unburnt fuel and ruin the catalytic converter prematurely. It will be either you save money on gas or save money on cat converter.

 

Huh? How do you come to that conclusion? Octane rating is a fuel's resistance to detonation. Higher octane allows advanced timing - once the fuel starts detonating timing gets dialed back. All the fuel should burn all the same unless the ECU goes into dump fuel mode to cool things down.

 

This statement was the reason for the following.

I didn't mean to insult, but saying that running low octane on a high compression turbo motor is just as good as running high octane is just not a true statement in the least. Nothing irks me more than people buying a high performance motor than trying to "save money" and go with low octane fuel.

I gaurantee that performance and fuel mileage is taking a good hit with the lower octane fuel. I'm sure they tested 87 in the car just to make sure that the various sensors and ecu would do their job when the car was subjected to knock induced by low octane fuel. You're not giving your mini a "treat" when you fill up with premium. You're giving the motor the fuel it was designed to run.

You don't need to ask or let a bmw engineer tell you why it would hurt your motor. You can just ask any real tuner/engine builder why it would hurt your motor and you will get a similar response from all of them. Also, making a motor capable of running low octane fuel isn't that hard at all. You merely need to have the computer add more fuel and/or retard ignition timing based off of readings from the knock sensor.

That is true, but if the ecu needs to alter (in this case lower) the compression of the engine you're losing power and efficiency. The first causes a harder hit on performance, the later a harder hit on gas mileage.

Actually there aren't as many sensors monitoring the engine as you might think. Now I haven't really gotten into looking into the mcs ecu, but if it works like most other ecu's I've seen it adjusts fuel/ignition timing based off of temperature, knock count, map/maf sensor, throttle position and 02 sensors. The knock sensor is really the only way for an engine to "tell" if you're on low octane fuel. This doesn't mean that the ecu actually knows you're running low octance fuel, it just knows that the motor is seeing knock when it shouldn't be based on preset maps/values that bmw has coded into the ecu. The knock sensor doesn't really work by sensing knock before a major event happens, the ecu looks for smaller spikes in voltage from the sensor. Once it sees those events the ecu assumes that a larger and more damaging knock event is going to happen shortly after. In a manner of speaking it does "sense" when a major knock event is going to happen, but it does it by looking for smaller less harmful events. If a major event were to happen before a smaller event took place the damage would be done since there is no possible way for the ecu to do anything after an event has happened. So it lowers ignition timing and generally dumps extra fuel in the motor, as rpm's go up it slowly increases ignition timing and removes fuel until it sees another spike. Essentially you're always "riding the line" since the ecu will constantly be adjusting, now if the ecu sees a certain amount of knock consistantly it may go into a safe-mode of sorts to prevent any extra damage from happening. However that kind of mode is generally reserved for something like a failed sensor.

I'm not trying to be an *** (seriously), I'm trying to inform people why running low octane fuel in a motor that produces more than 100bhp/liter is bad. Can you run 87 in your car? Yes. Will the motor like it and/or run as long as it would with higher octane? No. With lower octane fuel it is much more likely that you will have major knock events, even if the ecu has added correction in an attempt to prevent it.

 

Now this is the spirit and the request for the mathematicians: could you please provide a graph of costs of consumtion of premium fuel vs regular fuel with 10% Vodka content (in the fuel)?

How would one shot of Vodka for the driver a day effect both consuption and spirit?

I think keeping the driver boozed up will eliminate the worry about oil filter residue and lower fuel consumption as drinking and driving is illegal!!!

 

That would be something good to prove and quantify. I just think the BMW engineers that designed the ECU know more about it than "any real tuner/engine builder" and so far we don't have much info either way from them other than what's in the owners manual. I'll see if I can find more...

 

Here are two links, the best I could find. The first is the MINI press release about the new engines and the second about the new M3 V8 engine. Search for "knock". I have no idea if the anti-knock technology is the same in both but it gives an idea of what they can do.

http://www.motoringfile.com/2004/12/...ange_in_detail
http://www.nybmwcca.org/news.php?id=14

I assume you feel(and you may be correct) that the car is setup to not ride the edge of timing when running premium fuel. If we assume that both engines are always pushing the timing to the edge, would one edge be any more dangerous than the other? In fact it would seem that the high octane edge would be more dangerous if you suddenly picked up a bad batch of fuel from the tank. Maybe the car is tuned to an upper limit like 93 octane, then is 89-91 on the edge and wouldn't that be just as bad as riding the edge at 87?

It just seems you have faith that the system will adjust, as designed, or you don't. I have the faith. Try some 87 when you get your car! Get the faith.

 

I have the 2007 Cooper and had to go into Hassel Mini service, in NY, yesterday. I mentioned to the service advisor that I didn't feel that I was getting good gas mileage. I'm getting 20-22mpg in NYC driving (local).

He said that BMW recommends dropping the octane on the 2007 Mini even though the documents spec it higher. He said 89 would be fine and to see if I got better gas mileage with the drop in octane.

With everything I've read above I can't see how this could be true.

 

Are you talkin 20 to 22mpg IN NYC?? NYC is NOT "city" driving. That is running your car in a parking lot for 1/2 hour, for every mile you go.

 

Yeah, I hit a light ever couple of blocks. So 20-22mpg is normal? I get 40-42 on the Highway.

The service advisor felt I would get better mileage with 89.

 

20-22 mpg in NYC seems good to me. But what do I know.