Bigcoyote is (as usual) full of wisdom, and I would echo everything he says. I never attempted to change my pulley myself though.

On our Hyper Blue Cooper S we put in the Dastek Stage 1 tuning kit, which basically included a 15% pulley and a unichip engine management chip, which is exactly the same as what Bigcoyote has done, albeit in separate stages.

Our S was Dyno'd to 210bhp. Which for an automatic, which will always lose a wee bit of power in the drive-train, was astounding. If it had been a manual, we could well have been over 210bhp.

Admittedly, this time around we went with the full JCW kit rather than an aftermarket kit. It feels just as good, although we haven't had the car dyno'd. But at least this time we have the JCW supercharger which should handle the extra payload. Although as I understand it, the only difference between the standard SC and the JCW SC is that in the JCW SC the blades are coated with Teflon.

A.