I have been having bad problems this year with overheating my rear brakes at tight tracks like Gingerman and Autobahn. After about 25 minutes of driving, (with PSM off) I would get a completely squishy brake pedal, requiring pumping to get any braking done.
Strangely enough, the problem seemed to be with the back brakes. The calipers have turned a dark brown/purple color, much more so than the fronts. I was having to bleed the brakes at the beginning of each day, and the back calipers always seemed to have the air bubbles in them.
What could be causing this? I think it most likely was the "Active Brake Differential" feature, which apparently is on even when PSM is off. So, I recently went "mod crazy" and had the Guard 50/80 LSD installed, along with the Softronic ECU flash and Agency Power exhaust. I also found these brake ducts, which are Porsche OEM parts, from Vivid Racing:
Porsche OEM 996 C2/C4/TT Rear Brake Ducts 99-05 Image2
The Porsche PNs are 996-331-127-90 and 996-331-128-90, for the left and right duct respectively.
We had to trim the ends off a bit to get the ducts to fit around the cross braces, but they did attach to the control arms quite snugly:
The shields behind the rotors were also removed.
I tried all this stuff out at Gingerman this last weekend, and my brake pedal was solid the whole time. I attribute this mostly to the LSD, as the "brake diff" feature was no longer necessary. I tried running one session with PSM on with dry pavement, and it really cut in much less than usual. Turns 2 and 3 at this track usually cause a lot of "chatter" from PSM, but with this new LSD it apparently didnt have to intervene.
I cant really quantify how much these brake ducts helped my problem, but I figure its never a bad thing to get more air channeled towards your brake rotors.