i am looking for some help on a SC pulley for my 06 MCS. i want to replace the pulley to a 15% pulley to increase the power, but i am a little nervous. BMW desgined the SC for the MCS to be able to produce the best results for the stock pulley; making the engine spin at an optimual, and safe speed without burning up the supercharger. now why is replacing the pulley to make the engine spin faster without replacing the SC itself not going to hurt the SC or the engine? isn't this why BMW replaced the SC on the JCW in the first place; to keep the engine and the SC operating at its peak performance without damaging the interal bearings of the SC?

so if someone could enlighten me that would be great. if there are in physics nerds out there to help that would be even better; i am myself a math nerd (math major in college) so the mathematics behind it would be great, but if no physics nerds then someone with a good knowledge in this kind of thing is good to. so help would be great.

josh

 

think they're same sc just different pulley . do a search and you'll get lots of percentages and such to keep you enthralled for hours .

 

The supercharger on the JCW MINI is the same as the standard Cooper S in 05/06. The only difference is the pulley being a little smaller. Nothing else special about the supercharger.
I know your wanting to get a whole bunch of info and think about what pulley and why and analyze it to death. But in reality, just get a 15% pulley and put it on, You'll be happy I promise. Just look around you'll find almost everyone on this forum with an R53 has a pulley.

 

Don't worry about the math. The 15% pulley is the best mod you can do to your Eaton Supercharged MINI. Biggest bang and performance gain, for the bucks! Ford GT's are modded the same way.

 

It sounds like you are confusing two different things here...the supercharger pulley has nothing to do with the engine RPM, it only determines what RPM the supercharger is spinning.
In addition, Eaton is the company that designed the M45 that is on our cars, not BMW. I would have to guess that both companies gave their input on the casting design to our somewhat unique application in the R53, and i'm sure there was a collaboration of BMW and Eaton to figure out what size(stock) pulley would be used taking in to consideration the very broad spectrum of drivers all over the world.
The reason the JCW uses a different SC is because it has a smaller pulley. There are no serviceable parts from BMW/MINI for our M45s, it is sold as a complete unit, including the pulley. So because of that, the JCW units were built with the smaller pulley already installed. Apparently, BMW didn't want the techs to be swapping pressed-on pulleys when the JCW retrofit kits were dealer installed.

I hope that helps you understand a little better. Installing a smaller(15, 16, or 17%) pulley in place of the stock one is a nice upgrade A LOT of people have done with no issues and thousands of miles.

 

MINI reduced the size of the pulley from 65mm to 58mm for the JCW model; this is an 11.45% reduction. In the earlier models the JCW supercharger had a different lobe coating than the stock superchargers, but later stock superchargers shared the same lobe coating. The reason the supercharger was exchanged on the JCW version was because of the different pulley not because it offered a durability advantage.

There are two main drawbacks to overdriving the supercharger, one is the heat generated by the Root’s inefficient method of enabling boost. At a certain point (rotor speed), heat reduces density and counteracts the purpose of forcing more air into a given space, and the other is increased wear. Those two negative effects can be avoided by keeping rpm lower; a stock size pulley could cause the same issues if it was spun fast enough, say the 7.5k rpm region often.

In the past there were not many economical options for increasing output so overdriving the supercharger was the logical approach, I myself ran a 19% for 45k miles, thoroughly enjoyed it, and experienced no adverse effects. With tuning options available these days, overdriving the supercharger offers less of an advantage. For example, more can be realized through ignition timing and efficient fuel deliver if boost pressures and their associated heat (via Roots inefficiency) are not present to contend with. Of course the same tuning options can make the most of the inefficiencies as well, but why fight it.

After trying most of the reduction pulley sizes and a variety of tunes, I now believe the engineers got it right when they chose the 58mm pulley for the performance model. A heads up for you and the rest of the readership, a similar size pulley will soon be available.

 

Do it do it do it.
You won't look back : )
Do it do it do it!

The only (minor) geek-tech thing I'd add is that I prefer a steel pulley to match the heat expansion rates of the SC shaft, vs an aluminum one.

Good luck!
Eugene
2006 MCSa with 15% aftermarket pulley

 

MINI knew they were going to put a JCW model out, and deliberately left the supercharger pulley standard sized on the S so that the JCW could run a reduction pulley safely and have noticeable gains over the S.

Best mod ever - more SC sound, more fun, less tire tread

 

A similar size pulley will be coming out? Any details on that, k-huevo?

 

what is the ball park figure for installing a pulley on a supercharger? i don't want to get ripped off and i don't have much time to do it myself. i live in monterey, ca so if any one knows of somebody i could go to please let me know or if someone knows someone who lives in monterey that knows somebody, contact me on this posting page.

thanks everyone

 

 

I bought an Alta V1 (steel) pulley for around $100. I bought a smaller belt and cooler temp sparkplugs from NAPA taking advantage of a club discount. When my car came up for Inspection 2 (read: the expensive one) my dealer deleted the cost of parts that Inspection 2 included and essentially, the cost of install was a wee bit less than the cost of Inspection 2 by itself.

So it worked out to me paying for Inspection 2 and getting labor for the pulley install by the dealer for free. Warranty on my car intact.