Got a few questions, gonna try and break this down to make it easy.

I noticed in my search that there are a few different sizes S/C pulleys out there, 15%, 17%, and 19%. Seems like most people go for the 15% and I suppose my first question is why? Seems like the more popular option would be for more boost, so why don't many people go for the smaller pulleys?

Does the stock ECM have the ability with the 17% & 19% pulleys to compensate for the additional air properly without risking damage?

How can I ID the Pulley on my car? It's got JCW Tuning Kit badges on the valve cover, and I understand that the stock pulley removal tool will not work on these if mine has the JCW pulley. Mine doesn't not feel like it's got the power the JCW Tuning cars produce, so i just want to verify what I have.

 

The 15% is the most popular for several reasons. The belts last the longest, it's the most reliable as it spins the blower slower than the 16 or 17 and also is more efficient for track use. If you are going to track or race don't go smaller.
Lately more people go for the 17% as they want that little more low end it will give since it has a little more boost at lower RPM. But we do recommend changing the belt more often.
Due to the dual Map sensor system the ECU can keep up with any pulley and basic mods. Tuning is often over sold, but can net you gains later.
If you want a pulley you do need the shorter belt to have the right tension, and the cooler plugs to counter the extra boost. Check out our kit as it is just what you need.
http://www.waymotorworks.com/wmw-pulley-package.html

If you have a JCW tuning kit you should have the JCW pulley as that was one of the most important parts of the kit that came on the blower. it's hard to say how to tell the difference between it and stock as they look very similar, but the jcw does have lips on the front and rear of the pulley the stock pulley didn't. Here is a pic of the JCW pulley

 

Sorry about the delay and thanks for the prompt response! Very informative and a huge help. I was actually browsing your site, and a buddy of mine Jeff Benson has me doing some shopping around for some parts (I'll be doing a lot of work soon.)

I spoke to the dealer that sold and maintained my car and found the it IS a JCW Tuning Kit car, was an $8000 kit +install back in 2007. Supposed to come in around 210hp. The car does feel a bit laggy, so I had a buddy dyno it and only found 170Hp at the wheels. Disappointment! Looks like it's back to the drawing board....

 

Well the 200Hp numbers were flywheel HP claims from MINI, so 170 at the wheels is about right. So going to a 15 or smaller pulley will gain you a little, mainly in the low end torque as you'll have more boost at lower rpm.

 

PM'ed

 

We typically put 17% pulleys on JCW cars to make the effort worth it. Getting the pulleys off is a little more work, since the typical MINI puller tools are sized for the non-JCW cars. You may have to cut the pulleys off with a cutting wheel--something that should be done carefully so as not to damage the supercharger.