Hi,
Due to the quirks of the regs, a
JCW cooper might be fine, but an S could be failed. There are certain things that you are allowed to modify, depending on category. For instance in LMS (the highest level of mods) brakes are completely free, including ducts, you can de-cat the car, and do anything to the exhaust, but changing the supercharger is not allowed. A non turbo or supercharged 2WD is allowed the most latitude for mods, so that is how the cooper may get away with it.
Also, the amount of mods allowed varies to some degree on the age of the car. The regs are strictest for late moderns, ie post 98. That is why some early model GT-R's etc get away with more.
What is frustrating is that I don't want to win the comp, and never would even be competitive, despite mods. I just want to compete and have fun. However, in order to be accepted, I am resigned to the fact that I am going to have to put my pulley / air-box / headers and cat back to stock. This is annoying, but not really a big deal, and will take around 1-2 days work. I am sure we will still have a huge amount of fun with a stock pulley
Cheers
Robbo