spartansix

I have a RUF BTR 3.8 based on a 1991 965T which currently has the stock 3.3T brakes: S4 "medium red" caliper front on a 322x32mm rotor, and 964T rear calipers on a 299x28mm rotor.
In my possession I also have a set of 993 Turbo "big red" calipers which I know will fit on the front of the car, but I'm less sure of what my options are for the rear.

I have read that the 993 Turbo's rear caliper (S4 casting w/ two 28mm pistons) will not work on the rear of the 964 turbo because the 322x28mm 993 rotor doesn't work with the 964's parking brake.
Are there any other options for the rear of the 964 Turbo?

I understand that the actual braking performance of the 964 3.3 Turbo setup is likely more than adequate for anything the car might see, but my (admittedly stupid) reason for wanting to do this is that the 964 Turbo rear caliper on the car has a ridged face (as seen below) which works fine for the PORSCHE logo but doesn't work well with the larger RUF logos I want to put on when I refinish the calipers. Any of the flat faced rear calipers would work better for this: S4, 993, whatever.

Metal Guru

The last time I checked into this I think I determined that switching rear calipers wasn't worth the heartache.
I would send Bill Verberg a private message and see what he thinks.
Cobalt maybe will add his opinion also.

cobalt

The only option is to modify the face of the turbo rear or have smaller stencils made. The 993 N/A is made for a 24mm vs the turbos 28mm rear rotor width.

spartansix

Thanks guys, that was my fear. I guess I'll look for another set of turbo rear calipers and attack them with a file.
If I'm keeping the stock rears, it's probably not worth putting the Big Reds on as that will just move the brake bias even more forward.

Metal Guru

Actually it doesn't change bias in any way. I've been running Big Reds for over 10 years now. The biggest advantage is a small ability to disperse more heat through more swept area. They look cool too

cobalt

@spartansix Just curious if the calipers pictured are the ones you plan to use? The big brake caliper appears to be the standard 3.3T medium S4 caliper and not the big red/black. This would use the 132x48mm pad vs the big brakes 132x58mm pad. They both use the 44/36 pistons up front. FTI the three different setups require three different rotors. I am assuming you still have the cast iron uprights so the 94 turbo rotor would be needed for the big red/black vs the 3.3T rotor which has 10mm less material on the inside. You can see ho close it comes to the hat.

Visually you can tell by the top shape of the caliper.

Here is my 928GTS caliper on my C2. It is the same as the 94 turbo and 993TT front but the 928 is trailing vs leading mount so I had to swap the feeds and bleeds.

Metal Guru

I neglected to mention the pad size difference.
My Big Reds came off a 928GTS so they were black and the balance pipe was on the wrong end for my application.
Easy fix.

spartansix

@cobalt No, sorry -- the picture was just one I found on the internet to use as an example.
That said, the calipers on the car right now are the medium S4 calipers (current setup is all stock 964 3.3T brakes) but I have these "Big Greens" on my NA 964 that could be swapped over:


Not sure it's worth breaking up the green set for no performance gain though since I think the RUF brakes are going to end up yellow.

spjuvern

i still have the original 3.3 front calipers but would definitely want more bias to the rear even after deleting the bias valve.

cobalt

Why? If the back end is squirrely it might be your alignment especially with the 100% locking diff. If you want more rear bias on a turbo the only option are the 993RS rears but you need custom hats and rotors and lose your e brake.

I am running them on my track build but don't need an e brake for track duty.