I have a 2004 cayenne turbo with 18 inch wheels and was wondering if the larger rear rotors used on the turbos S or the E81 powerkit would fit my stock calipers or are the calipers on those vehicles larger and I would need other supporting parts as well.

 

your stock calipers will not fit over the bigger rotor and bolt in place.

not worth the upgrade to maintain Turbo S brakes when they wear out.

 

In regards to trying to fit 380mm calipers on the front, versus stock 350mm I know that 19 inch wheels are minimum but is it possible to fit 380mm calipers under 18 inch wheels if spacers are used.