I am thinking about getting a 15% or a 19% pulley. But would the 19% lower my MPG and increase my RPM? lets say if in going 70 MPH at 3,000 RPM stock. Would the 19% pulley cause it go run at a higher RPM at 70 MPH?
Same question with the 15%
Thanks

 

No, making the supercharger pulley smaller has no direct affect on engine rpm, it only increases the amount of boost (increases the supercharger ratio) and shoves more air (and fuel) into the engine at any RPM. I doubt you would notice any RPM change at a given MPH. You're not doing this as an 'economy mod'.
-BM-

 

RPM same

MPG down

Boost up

Fun UP!

 

I want a smaller pulley too. How much worse is the MPG?

 

It's not too bad, the trick is keeping your foot out of the gas with the new found power...

I dropped about 1 - 2 mpg in normal driving mode...

 

Didn't notice much difference in MPG w/ my 19%. Although I did notice how much quicker the car is

 

The only difference when off boost is parasitic drag. The 19% would create more drag because it's spinning the SC and water pump faster. I haven't found that my 15% has dropped MPG noticeably. With the 19% you do need to be careful to stay away from the redline, as at that RPM you are at or above the SC RPM spec.

 

With 15% I didn't suffer any mpg loss contuning to drive normally.

 

That's the key. No matter how much pulley reduction you purchase, you should see no reduction in fuel consumption under normal driving conditions. This should be especially true on the open highway.

Your best bet is the 15% pulley. You can still use the stock 330cc injectors with it. 17% and 19% will require more fuel at WOT, and you will need at least the JCW (380cc) injectors. Heat soak will also become more of an issue with 17% or higher; you also won't really see much of an improvement unless you upgrade the head for more airflow. If memory serves, for 17% or higher, you have to purchase the reduction pulley for the alternator, or you will prematurely wear it out.

Get the 15% pulley, CAI, Invidia exhaust, and tune, and you will have a nice Stage I MINI.

 

What happened to the River City Mini Club? Did they fold?

 

If the only pully you change is the SC, then the belt will run at the same speed...if you change the diameter of the crankshaft pully/damper, then a change of pully size on the alternator would becadvisable, but not required.
You can get to a 17% or a 19% reduction with just a sc pulley, or a sc pulley, and a crankshaft damper size change....a -15+ a +2 is roughly a 17, a -17% and a +2 is roughly a 19....
A 19% reduction is pretty agressive, and might not be well suited for many folks, or for many mini motors...they are getting upthere in miles, age and wear....15% are very safe, 17% are now generally safe... Many have done 19%, and removed them....some kept them...

 

IMO if you run more than a 17% more fuel is a must...17 with stock injectors are ok...lean at higher rpm's perhaps, but if you run red line much, the 15% is better suited to you.

 

apexer, yes, River City MINIs disbanded over a year ago. HR MINI is the only club around; there is no more Seven Cities MINI either. We usually catch up with some of the River City members when we do our annual Cooper Vineyards run in July. We're shooting for June next year to try and beat some of the heat.

Next would be either Tar Heel MINIs or DC Metro MINIs.

 

To give the op a bit of an answer...
You car's motor will run at same engine rpm with a pulley on...what changes is the speed of the SC....
Many folks get "about the same " mpg once they learn not to use their foot as much...if you do jackrabbit starts...you will burn more fuel. Drive the same as you do now...and you will find you have more pep for when you want it, and about the same mpg with a 15 or 17...
If the intake charge gets too warm, the mini's computer will enrichen the mixture...add more fuel to prevent engine dammage from detonation...and the side effect of a pulley is more heat since the SC is running faster/less efficiently.....so I'm iffy about saying the same with a 19.
Also octane is more important with a pulley...93 becomes pretty important with a 17% to prevent retarted ignition timing...
It has been stated that a 15 with CA 91 octane will be running retarded a bit...
IMO do not even consider a pulley unless you always use premium fuel...a stock s might get away with 89-90...might not, but with a pulley...a disaster is wating to happen...an expensive one too...

 

I lost 1-2mpg like previously mentioned with normal driving.

 

IMHO, I would steer clear of the 19% pulley, a lot of people have had trouble with them, specifically with belts, I believe...

I run a 15% pulley and an intake and not much else, and I like the power increase. I didn't see too much of a MPG drop. My ex's car had a full RMW workover and had a 17%... I never calculated her MPG. But her car... Oh man does it pull

If I could do it over again, I'd get a 17%. In fact, I might have to have Helix switch it one of these days... I have a press-on model, so no more messing about with the hub, anyway.

Ninja edit: IF you do rev out your engine every once in awhile and you're thinking about getting a tune like the one Jan does, I'd probably stick with thee 15 or at most the 17%, because the redline is moved up significantly (at least on a Jan tune... you have a new redline of 7300). Just something to keep in mind for the future.