1st Gen R53 Cooper S Most liked posts in thread: Question concerning underdrive pulleys

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Get the proper sized crank puley.

 

No experience, but yes the alternator is going to spin slower. Your supercharger is going to spin faster. You got a 15% pulley to be safe over a 17%. Now you are going to be somewhere near the same as the 78%.

If it was Me I'd call Way & have him swap you a stock sized PWR damper for the undersized one. You have plenty of time to make the exchange before your pulley install.

 

I think this is what he got from Way.

PRW 2510901 FluidGel Black 8.7 Percentage UnderDrive Serpentine Pulley Damper for BMW Mini Cooper, 2001-2006 Gen 1, Tritec 1.6L : Amazon.com : Automotive

This is the stock sized one.

PRW 2510900 FluidGel Black 138mm Serpentine Standard Drive Pulley Damper for BMW Mini Cooper, 2001-2006 Gen 1, Tritec 1.6L : Amazon.com : Automotive

 

I would only run the stock size.

 

For me it would be turning the supercharger too fast. I went with a 15% pulley, because I intended to use my MINI on the track occasionally. From what I had read it was recommended to go with a 15% for that use. The 17% was said to be fine for street use, but not so fine on the track.

If I remember correctly the OP said in another post that he wanted a 15%, because it was safe. His MINI is high mileage so I agree with his thoughts.
Going with an under-drive crank pulley will turn the Supercharger faster than just the 15% with a stock sized crank pulley would.

 

8.7% underdrive crank pulley? You sure about that? Never heard of such a thing. Most people use 2% OVERDRIVE crank pulleys

 

Why would they make such a thing?

 

And why is that?

 

I understand the confusion since both are listed. Good to know Way sent you the one you wanted.

 

Glad it got sorted, I couldn't see a reason for it either, wonder if it was designed for a different veh. & just happens to fit our engines so they cross advertise it that way.

Under Size Crank Pulley = Slower Accessories
Under Size Accessories Pulley = Faster Accessories

 

If you tell me diameter of crank pulley I can suggest to you exact pulley size which will match to your mods and wishes. A big range of pulleys is from -11 up to -20%.