Hatzenbach

OK this is a bit of an unusual question and a long shot, but maybe someone knows the answer.

I recently wanted to upgrade my front rotors on my 997.2 C4S from the 330 mm diameter rotors to GT3 (350 mm) rotors.
Both of them are 34 mm thick, so that should be no problem.

Should be an easy upgrade:
In order to compensate for the wider rotor you need caliper spacers and longer bolts.
It was a bit of an ordeal to get the spacers and the bolts (several missing shipments), but eventually I found them here on rennlist.

OK, after receiving all the parts I replace the old rotors with the GT3 rotors.
And they don't fit :-( Here's the odd thing: The rotor itself "sticks out", meaning it no longer sits right in the middle of the caliper but the outside of the rotor actually touches the inside of the caliper.

After lots of measuring I found out that the top part of the rotor hat (the one with the 5 holes) is 6.34 mm thick at my stock rotor, but 7.55 mm thick at the GT3 rotor. That now has the same effect as if I had inserted a 1.21 mm spacer between the hub and the rotor. And that means that the rotor disks themselves are off center by 1.21 mm (just enough to make contact with the caliper). Again both rotors have the same thickness (34 mm), so that's not the reason for the problem.

So here's the question: Is that normal (are GT3 rotor hats thicker) or do I have a bad pair of rotors?

semicycler

Pretty sure ceramic rotors have different hat sizes between models. Therefore iron rotors would be different too. Try asking in the GT2/GT3 forum or Turbo forum. They should know more about rotor and hat differences between models.

mdrums

Use Turbo 350mm rotors and they will fit perfectly with 997 GT3/Turbo calipers. This is the brake upgrade I did on my GTS which is basic Carrera S 4 piston and 330mm rotors.

The uprights on a GT3 are very different than Carrera based 997's...the Turbo uses the same upright as the Carrera S...so the turbo 350mm rotor and GT3/Turbo 997 6 piston caliper is direct bolt on.

Hatzenbach

Thanks, and yes the guys on the Gt3/Gt2 forum confirmed that:
https://rennlist.com/forums/997-gt2-...-2009-c4s.html

Now I need to find a buyer for my GT3 rotors ;-)\

Hella-Buggin'

Now, are the uprights the same for a C4s? I'd hate it to go through this again Chris.

mdrums

Turbo's are all wheel drive and Turbo rotors fit Carrera S and GTS...all have same uprights...they will work.

Please know you all will need the Porsche 6 piston calipers...you can't just go using the 350mm Turbo rotors.