Trying to research why pulley and why the different percentages. I find the why.... more hp. But why one percentage over another?

 

15% is by the most common
16% was created for marketing as some wanted more than 15 but not a 17.
17% will get you more low end torque as you will be spinning the super charger 2% faster at lower rpm.

Basically if you are just the normal person that wants a bump in power a 15% will be perfect and give you the best bang for the buck.
If you are tracking the car you also only want a 15%, going smaller will over spin the supercharger during the long track runs and actually cost you power
If you are that person that just daily drives your car and has to have the most right off the bat, but doesn't run in high rpms alot then the 17% can work for you.

We offer them all, but again I personally run a 15% and is what most use still
http://waymotorworks.com/wmw-pulley-package.html

 

Great. Thanks.

 

It all has to do with heat. Smaller pulley equates to more boost that makes the air going through the intercooler hotter. The stock intercooler does not have enough area to dissipate the additional heat. The 17% gets to that point with sustained high RPMs.

Way sells parts, repairs MINIs and drives MINIs. In other words, he knows what he is talking about, IMO.