Since the introduction of the Cooper S in 2002 people have been finding new and improved ways to gain horsepower. New exhausts, upgraded air intake systems, modified ECUs and a host of other additions can help satisfy that lust for more power. Yet there’s one magic bullet in the MINI aftermarket that is head and shoulders above the rest in creating power: the super charger reduction pulley.

Warranty and Reliability

Before I get to the actual review, let me touch on what a reduction pulley does and how address a few concerns owners may have.

The principle isn’t new. Simply decrease the size of the stock supercharger pulley and you’ve got yourself a more powerful Cooper S. Dynos show gains on a 15% reduction pulley (the most popular size on the market) can over 15bhp. So with one modification your stock 170bhp Cooper S can go to 185bhp. And it gets better. The Webb Motorsports 15% Pulley tested retails for only $120 (other pulley’s msrp for about the same).

So you may be asking, where’s the rub? How is it possible that something so cheap, simple and small can add so much? The first obvious concern is warranty and reliability. The reliability question is easy when it comes to a 15%. With the JCW upgrade using a 14.6%, it’s obvious that the 15% falls well into the safe category of modifications. With MINI testing and re-testing the JCW pulley size the world-over, you can expect a pulley .4% smaller will perform the same. In fact to my knowledge (and I may be proved wrong in the comment section at some point) there hasn’t been one case of mechanical failure that was the direct result of a 15% pulley.

Now onto that pesky warranty question. MINI has left it up to each dealer and then it’s regional reps to determine if and how a pulley may have effected any mechanical failure. While I’ve never heard of this actually happening, it is technically possible for a particularly uninformed or ignorant MINI Service Advisor to use the appearance of a reduction pulley as a scape goat to deny warranty coverage on a few related internal components. It’s rare but it has happened in a few cases. To deny warranty coverage on the entire car due to a reduction pulley is just about unheard of.

It may be worth mentioning that Webb Motorsports warranties their Pulley for 2 years/24,000 miles or the remainder of your factory warranty. Some other vendors offer similar warranties.

But enough about who covers what, let’s talk performance!

Webb Motorsport Pulley Performance

Wow. That was all I could say after my first test drive. The car was eager, quick, and pulled hard all the way to redline. I could feel the difference immediately and it was impressive. In fact I was toying with simply having one word for this entire section of the review. For the longest time I couldn’t think of anything more to say than; wow.

Think about how much fun it is to row through the gears of a Cooper S from 0-60. Now add 15hp throughout the entire powerband. Or consider this; from a standing start with DSC off my Cooper S with a JCW intake, Supersprint exhaust and now the 15% Webb Motorsports reduction pulley, will put a healthy amount of rubber down in first gear, second gear, and (if I wasn’t there I wouldn’t believe it) third gear. The car feels more eager and pulls hard all the way to redline (which by the way you’ll want to watch out for a bit more with a 15%).

Or you could just say; wow.

Webb Motorsports Pulley Design

Randy Webb has been installing and designing pulleys for four years now. First it was in conjunction with Alta. However now Randy has his own design and it features a couple of unique design traits. Here’s how Randy explains his pulley design on

>First, it is all steel. What that means is that the thermal expansion rates are the same between the pulley, the hub of the pulley, and the shaft of the supercharger. That becomes very important when the temperature deltas can vary by as much as 300F. The same thermal expansion rate means you won’t have to worry about the stability of the taper bore fitment on the shaft, or the tension between the hub and pulley.

>Secondly, it is stainless steel, so the unit will not corrode over time like aluminum and mild steel do.

>Third, it uses a positive stop on the inside of the pulley, so the hub is always in the right spot.

>Fourth, the end of the pulley is capped, so as long as the hub is pushed all the way onto the shaft, the pulley will always align itself as it pulls the hub into itself. After having done over 800 pulley installs, I have never seen more than .02″ difference between these – the belt is always perfectly aligned.

>We have several unique features on our pulley as well. We have machined a center hole to both reduce weight, and allow for easier tolerance checks. We have also worked hard at reducing the radius and therefore rotational mass.

>Finally, this is a taper bore style pulley, rather than a heat and press interference type pulley. This pulley is installed at room (or shop) temperature.

As you can see in the picture at the top of the page, the Webb Pulley is almost jewel like compared too the stock piece. It’s truly a piece of art.

The Pulley Conspiracy Theory

As part of the design process for the pulley, Randy Webb did some research into this subject (w/the help of Eaton who manufacturers the MINI’s supercharger) and found that a 15% reduction is really the optimal size in regards to the powerband. So this begs the question; why didn’t BMW simply give the Cooper S a smaller pulley from the start? There are a couple of theories. The one I subscribe to goes like this: BMW didn’t want to increase an already large power gap between the Cooper and Cooper S. They also wanted to protect the low-end 3 series and the (at the time) soon to be released mid-range 1 series. By capping power on the MCS to 170bhp they are able to slot it in nicely the other cars’ offerings. They also give the JCW plenty of room at 210bhp. Helpful when you’re charging around $6,000 for the Works upgrade. Again this is all just a theory, but I know quite a few people in the industry that believe it.


The Webb Motorsports Pulley is an addicting, neck snapping addition to the Cooper S that simply can’t be matched by any other modification I’ve experienced. With very little to be concerned about in regards to warranty, it’s an addition that shouldn’t be overlooked when modding a Cooper S. While it doesn’t turn your car into a JCW beater, it gives the Cooper S the power that it deserved out of the factory. It’s like flipping a extra special secret switch that MINI doesn’t want you to know about. It’s also just happens to be the first product to ever recieve a perfect score in a MotoringFile review.

MotoringFile Rating: 5 (out of five)

Where to Buy: The Webb Motorsport Pulley retails for $120 and can be purchased from Webb Motorsports. Several other MotoringFile sponsors carry a similar pulley as well. Promini, Helix, Outmotoring and MyMini all carry 15% pullies and M7 carries their own 16% design.