Is there a document/specification somewhere that identifies the various specifications of Porsche biasing valves? I'm having a hard time getting more braking to the rear since putting Big Reds on a S2. Thanks

 

The stock 944S2 valve is an "18/5" valve. The changeover pressure is 18 bars (260 psi.) Below this pressure, you get equal hydraulic pressure to the front and rear brakes. Only 50% of the pressure above changeover pressure is transmitted to the rear brakes. The "5" refers to a reduction factor of approximately 0.5, which is actually 0.46 or 46%. Other biasing valves used by Porsche include the 33/5 (928, 944S), the 43/5 and the 55/5.

If you have Big Reds on the front and stock calipers on the rear, you have changed the inherent brake bias towards the front. If it is too front-biased, no proportioning valve is going to correct this. For example, if you simply delete the proportioning valve, you will get 100% of the hydraulic pressure to the rear brakes. If this does not give you enough rear braking, you need to play with the inherent bias by either increasing the piston size of the rear calipers (i.e. move the old front brake calipers to the rear) or by going with more aggressive (higher coefficient of friction) pads in the rear.

You should probably ask for the experience of others who have gone to Big Reds on 944s, if you haven't already.

 

I use 5/45 bar on mine with Big Reds front.

5/33 # 928.355.305.02
5/45 # 964.355.305.00

 

That a lot of help guys - I've read several old posts and this is very useful. Thanks