I'm going to show off, once again, how little I know. :smile:

I've read that the stock MCS runs rich, and putting a -19% pulley will make the car run lean. Does that mean I should get better MPG with the new pulley?

 

if you don't stomp on the gas all the time.

 

I wish i was rich and lean.

 

>>I wish i was rich and lean.

ephedra and junk bonds...

 

Even on a fully stock MCS I swear I can see the gas needle go down when I stomp the gas. :smile:

Seriously though... The way I understand it, rich means it is burning more gas than it needs and lean is the opposite. Thus the MPG should go up. Right?

 

Not necessarily. A car running with a lean mixture will run hotter (which ultimately decreases efficiency) and runs a greater risk of detonation (AKA pinging). Generally speaking, you don't want to run too lean as you can do substantial damage to the motor over time. Pinging sounds cute and innocuous but in reality it does bad things to your pistons. I'd imagine the ECU would compensate for a lean mixture by retarding the ignition timing as well, which has a negative effect on performance.

At any rate, it's not something you adjust to increase mileage unless you're running horribly rich already--which would indicate another problem, likely traced to some engine management sensor or other.

 

So is putting a -19% pulley in a completely stock MCS a bad idea? I have plans to do other mods, but money is tight and will be a while before my next mod (such as intake or chip upgrade).

 

I didn't know a -19% pulley will make your car too lean? If you have the correct chip tuning where it leans out your car slightly but still on the safe side, I'm sure you might see a little difference in gas consumption, that is, unless you have heavy feet all of a sudden.

I believe the one case where the car runs lean was JLM's car because of his injectors not being able to deliver anymore close to redline. So it can't maintain the mixture, BUT he has done many, many mods to get to that point, so you shouldn't worry.

 

By the correct chip tuning, do you mean having an aftermarket one? Cause I have the stock programming. Everything is stock so far, and I am considering the 19% pulley.

 

>>So is putting a -19% pulley in a completely stock MCS a bad idea? I have plans to do other mods, but money is tight and will be a while before my next mod (such as intake or chip upgrade).


I don't know one way or the other if it's bad. Lots of people seem to do it to no ill effect, and I've read that the MINI is programmed on the rich side of the scale anyway...so I guess there's enough leeway to compensate. That said, you've got to consider the system as a whole...each piece is designed to work with the other and so forth. Change one piece and what happens to the system? That's the question.

You'd probably do best to speak with the shops and individuals who have really done their homework on the pulley mod (Randy Webb, Helix, etc). They'd be able to tell you much better than an armchair quarterback like me.

 

>>I wish i was rich and lean.

:smile:

 

The MINI runs very rich and adding any pulley (19% included) will "lean it out" meaning it will make it less rich. Ideally, you do not want it rich or lean to get the best performance/efficiency.

From what I understand, the MINI does have a knock sensor to sense if the engine is running too lean but I don't think you'll have any problems, especially if all you do is the 19% pulley.
-Chris

 

Here's an explanation of fuel trim I wrote a while back:

There are several different learned adaptations that take place, but the most significant and noticeable is fuel trim. Here is an explanation of fuel trim and what it does for us.

The DME controls Air/Fuel mixture in order to maintain power, efficiency, and emissions. A/F is expressed as either a ratio (14.7:1 for example) or as a Lambda value. With iso-octane ("ideal" gasoline), Lambda of 1.0 is equal to 14.7:1 A/F. This is known as "Stoichiometric", a condition where there is a perfect balance between oxygen molecules and the various hydrogen and carbon based molecules in petroleum. With the oxygenated gasoline that most of us use, actual A/F ratio of 15:1 is closer to stoichiometric.

If Lambda is greater than 1.0, then there is a surplus of air and the engine is running lean. If Lambda is less than 1.0, then there is a surplus of fuel and the engine is running rich. It should be noted that the ratios are mass-based, not volume-based.

So, why don't we always run at 1.0 all the time? Well, we do MOST of the time. At cruise and idle, mixture is held tightly to 1.0 to keep the catalytic convertor at optimal efficiency, so the emissions are minimized. However, when we need acceleration, the mixture gets richer. Why? Maximum power is made between 0.85 to 0.95 Lambda (12.5 to 14.0 A/F with iso-octane). So, under acceleration, mixtures get richer. Sometimes you want to get even richer under acceleration to keep detonation (pre-ignition of the mixture from excess cylinder temperatures) away. The MCS engine, which has a relatively high compression ratio for a supercharged engine, which especially under lots of boost, is very succeptible to detonation).

So, now that we know that the ECU wants to be able to control the A/F ratio. It has a prescribed set of values (maps) for a given RPM, Load, etc. So, the DME tells the injectors to pulse for exactly XX.X milliseconds and that SHOULD get us the proper A/F ratio that we want. Well, if you tell an employee to go do something, you want to make sure they actually did it, right? The ECU has some snitches (the front O2 sensor and the MAF, for the most part) that will report back whether or not the desired mixture has been attained. The rear O2 sensor is used mostly to monitor the condition of the catalytic convertor, although in some applications it also contributes to trim information.

Based on feedback from the snitches, the DME learns to apply a correction factor to its commands to the fuel injectors. If you know that your employees take longer than the standard allotted time to do a specified job, you will need to adjust for that in your planning (injectors are in a union, so it is tough to fire them). The learned values go between the maps in the ECU's Flash ROM (the "chip&quot and the signal to the fuel injectors. These learned compensations are known as "trim". So, when you see "trim", it means "compensation".

"Add" means additive trim, which is addressing an imbalance at idle. When the ECU is using additive trim, it is telling the injectors to stay open a fixed amount longer or shorter. The malfunction (e.g. vacuum leak) becomes less significant as RPM increase. For additive adaptation values, the injection timing is changed by a fixed amount. This value is not dependent on the basic injection timing.

"Mult" mean multiplicative trim, which is addressing an imbalance at all engine speeds. The malfunction (e.g. clogged injector) becomes more severe at increased RPM. For multiplicative adaptation values, there is a percentage change in injection timing. This change is dependent on the basic injection timing.

FYI, I am currently running the 19% with stock ECU.

 

>>Here's an explanation of fuel trim I wrote a while back.....
>>

thanks for this well written informative post.

 

I have an 05 MCS w/15% pulley and JCW intake, Denso Plugs. Problem when cruising in either 5th or 6th and I stomp on the accelerator I am getting "pinging" or detonation. I actually noticied this even before the pulley upgrade a week ago. The car runs "rich" stock so I would assume I would not have an issue with pulley...

Question: Should I be running Super Unleaded?
Question: Would upgrading to the Cooperworks software solve this problem since it would factor in the extra air?

 

I suspect that resetting the ECU would help. If you've read the entire thread, you'll see that your car has "learned" how to compensate for variations from the "ideal" set up. You've made a big change in your car's engine configuration, but the ECU is still using information it learned based on data from your original stock setup.Resetting the ECU will cause it to start over again with a blank slate.

The quick and dirty way is to just disconnect the positive battery cable for at least half an hour. (I think.) But this resets a bunch of other things you may not want reset. There's another way of doing this via "test codes" and the speedometer readout. A search for threads with "reset" and "ECU" should turn up the info.

 

I'm sure running Super would definately help also, what are you using right now?

 

Even if the mixture is more lean than with the 15%, you're stuffing more air into the motor, and the ECU will squirt more gas. The lean condition can arise if the motor can't squirt enough gas. As you do more power adders, at first you're fine as the stock programming is rich, and can compenate over a bit of range. But if you really stuff tons of air into the motor, eventually the injector can't put enough fuel into the airstream, even if it's open all the time.

So when that occurs, the normal trick is to increase the fuel rail pressure and maybe the capacity of the fuel pump. This is where people start in the ford EFI world. Then comes larger injectors. This seems to be where many start in the Mini world, although Dinan appears to doing the pressure tricks.

To sum up, mpg is really a function of fuel flow in mass per unit time and car speed. A/F ratio is a molecular ratio, and is independant of vehicle speed. To approximate,

Mass of gas per unit time is proportional to a/f ratio * rpm * displacemect* volumetric efficiency,
so MPG is proportional to Speed / Mass per unit time.

adding the pully increases the volumetric efficieny, so all other things being equal, MPG goes DOWN with increased SC compression.

After reading this, I fear I',ve just made things worse....

Matt

 

Ive run both the 15% and the 19% with stock and after market MTH programming and did a few A/F test. One major thing to remember when your crusing at hwy speeds you not on the SUPERCHARGER at all! therefore it doesnt make a diff which pulley you have. MPG will be the same along with the rich/lean condition. So far im pretty much the MPG champ with over 526 miles on a tank. According to Mapquest thats how far it is from my house to the Hotel i say at during the Dragon run weekend. Which ive gone there in Stock, 15% and the 19% pulley on one tank and still could drive around once there. The difference come in when your acturally using the SC for each higher percent smaller pulley it kicks in sooner so your are running leaner than before, but even with 19%, exhaust and intake no other changes (with mine atleast) it was creeping to a lean mix near the end of the run 5800-7200 but it never ran lean. If i did the extra work like JLM did to make his intake side more effecent then i may have a problem of running to lean. The other part is that since with the smaller pulleies your pushing more air there for the car is going to pump more gas causing decreasing MPG and that is if your on the SC in the first place.(hard not to do i know )

Every racer, tuner etc. out there has their idea of how they like to run there cars. With Sayiing like "Lean is mean but Fat is where its at". personaly i like a very lean idle and first quarter of the rpm range for quick takeoffs. From there its slightly rich for the next half then a bit more rich (Fat) on top end so i can maintain the high rpm with less fear of blowing the engine. I had the attitude that you must "First finish before you could finish First"

 

I run Super but here in Cali sometimes that can get freakn' expensive So I use middle grade. I will talk to the tech and see what's up?

 

We have pretty crappy gas in CA. So you're already octane starved. Why get a blown car then run cheap gas? Doesn't the S reccomend 91 min? This will get even worse with pullys.

Matt

 

Indeed, from my readings, with US gas, 91 is the minimum, and generally the best we can get in CA... For a tank of gas, to save maybe a buck or two (compared to 89) just isn't worth it, imo...

 

Thanks for the explanation! (I love this forum)

 

You get 526 miles out of a tank? I'm lucky to get 325.

Dr Obnxs... You did make it worse. But with me, that is not hard. I guess the important thing to remember with the SC pulley reductions is that you are not reducing or increasing the amount of gas being used. Just increasing the amount of air.

 

Do you have an A/F meter in your car and if so which one?