Is anyone here using S4 front calipers (or 993 fronts) on the rear with P/V????

[Leo]

Please let me know. I used to have a turbo with big reds on the front and S4 on the rears.
TIA

[Bill Verburg]

It's unclear what you are hoping to learn, Perhaps some clarification is in order

[Leo]

Bill,
I used to have a 1986 RUF BTR that had an interesting setup. It had big reds on the front and 928 S4 front calipers on the rear. I took this car to Sebring once and I was very impressed with the braking power, far superior than turbo brakes. It also had a brake bias adjusting knob. I'm including photos here.
Thanks Again Bill.

[Bill Verburg]

Originally Posted by Leo

Bill,
I used to have a 1986 RUF BTR that had an interesting setup. It had big reds on the front and 928 S4 front calipers on the rear. I took this car to Sebring once and I was very impressed with the braking power, far superior than turbo brakes. It also had a brake bias adjusting knob. I'm including photos here.
Thanks Again Bill.

The front certainly looks to be a 993tt/RS 322x32 aka 'Big Red' this would use a 132x75mm pad

here are 3 axle sets of pads, from back to front 993RS/tt front, 993RS/tt rear, 930/964 f/r S4/944trear


hard to make out the back

There are several possibilities, Hopefully it is not an S4 front but because of the rotors and adj p/v I suspect that it is S4 front in back. If so hopefully the rotor is a 304x32 if it's a x28 then when new it is below spec for that front caliper.

There are 5 calipers that use the same 132x72mm pad(middle ones in the pic), S4 front, 964RS/3.3964t, 993RS rear, 993tt rear, 993 front

they different is several ones
964RS/3.3t are radial mount, 36/44mm pistons and have integral stands for use w/ 322x32mm rotors

S4 front and 993 front are radial mount, S4 is trailing mount, 993 is leading mount, 36/44mm pistons for use on 304x32mm rotors. These don't have the integral stands that the above have which is why they use a smaller rotor(usually)

993RS is an axial mount(has ears) 30/36mm pistons and is narrower than the above for use w/ 322x28mm rotors
993tt is the same as the 993Rs but has 28/28mm pistons

The performance will come from 993RS on 993Rs rotors, here is a list in order best to worst
@70bar line pressure the brake torque in n-m, ratio
993RS 2306/1618, 1.426
930 1961/1242, 1.579
993tt 2306/1155, 1.997
993RS front/ S4 front 2306/2381, .969

All of these come w/ p/v(except the 930)which would reduce rear brake torque above ~55bar line pressure, all can profit by removing the p/v except for the last one which needs an aggressive p/v

Some questions
size of your rear rotor? diameter x width
axial or radial mount?
parking brake? yes/no
piston sizes?