I’m thinking of upgrading the brakes on my 1994 964 C4 factory Turbo Look. The car is primarily a DE track car. This is my current set up.
• Front: Stock calipers 40/36 pistons, Zimmerman drilled rotors stock size 298X28, Pagid orange pads.
• Rear: Stock calipers 34/30 pistons, factory Porsche 3.6 Turbo drilled rotors stock size 299X28, Pagid orange pads.
• Proportioning valve (PV): Stock 33 bar which has a reduction factor of .46
(I got the specs above from Pelican Parts web site http://www.pelicanparts.com/MotorCity/wmv/brakes.htm )

This stock set up with Pagids works well with one problem. The rear brakes run much hotter and wear faster than the fronts. I’ve been told this is a result of the normal front calipers and rotors, the relatively large rear calipers and the 33 bar PV found on the C4 factory Turbo Look. I have no lock up problems. I’m looking at ways to add some stopping power and equalize the braking effort some to take some of the stress off of the rears.

One thought is go to Big Reds (44-36 calipers 322X32 rotors) in the front and change the PV to 60 bar. This is the exact set up as the 94 3.6 Turbo, so I assume this would be a balanced set up. Another thought would be to go with Big Reds in the front and move my current front calipers to the rear, but I don’t know what PV to use with this combination.

I don’t know how to calculate the “reduction factor” which the PV seems to dictate along with the size of the calipers, pads and rotors I suppose. The “reduction factor” for ALL the set ups on Pelican web site is .46. I assume I should try to come up with a PV which would give me the .46 “reduction factor”. Does anyone know how to calculate the “reduction factor”? Or…am I all wet with this line of thinking?

Help please!!

 

If everything else is fine, ie no overheating, adequate performance etc.

Is changing the rears more often that bad?

If you want to, just change the fronts and p/v to either 3.3t spec w/ the 993calipers and 322mm turbo front rotors

or

the 3.6t spec w/ Big Reds on the same 322mm rotors, this set up is available as a kit for ~$1500-$1600

there are 2 critical #s for a p/v the reduction factor. all Porsche use .46 and the knee pressure.



In this diagrm you can see the effectt of theses #s, the knee is where the p/v starts limiting the line pressure the reduction factor is how much.