Dave White

Car is in the shop for some of the final upgrades and maintenance. I needed new rotors and calipers probably needed rebuilt, so I decided to upgrade. After doing tons of research, thanks especially to Bill Verburg for tons of shared info, I still have a question on which, if any, p/v should I use.

I have an 89 C4 that is set very low and stiff with JIC's, running 7.5, 9 x 17" wheels with street tires(non R compound). I will be using 928S4 fronts with 304x32mm drilled rotors and drilled standard sized rears with a 993 30/34 caliper. I don't do any tracking as of yet, but may this year.

Any experience with this setup and what works or doesn't would be appreciated.
Thanks in advance!

Frank 993 C4S

I have 928 GTS (same as 993TT - not S4) set-up in the front on the 993 C2 caliper in the rear. The stock proportioning valve is great and I didn't touch it. Best part is that front and rear brake pads wear evenly, i.e. get always replaced at the same time. I use the car mostly on the track and it is an RSA.

For more details see here:

https://rennlist.com/forums/964-foru...e-upgrade.html

Dave White

Thanks for the reply, good info on the pads, but your car is naturally more front biased than mine will be with your big reds/blacks vs my mediums on smaller rotors. Maybe I will need less rear biasing?

ThomasC2

Replace it with a Turbo valve, think it's 55 bar. Part.no 965.355.305.01

I did this at first, but later on I removed the valve all together and just connected the pipes without the valve as they did on the Cup cars. Works even better. Makes the car more stable under hard braking and the pad wear is more even front/rear.

Thomas

Bill Verburg

You will have in essence 993 brakes, why not use a 993 40bar p/v? though I doubt that there will be issues if you keep the stock 55 bar version

Dave White

Thanks Bill, I didn't realize they used a different one for the 993's. I guess I'll start stock and go from there, then maybe to the 40.

If anyone else has comments that is using my setup, I'd still like to hear them.

f@tboy

Yes, I did exactly this too.

carrera

Anyone else remove their proportioning valve ?
Were the results to your liking?

Marc Shaw

I removed (gutted) the p/v as per Garrett's DIY and love the difference (993T front calipers and 964Turbo rears).

Marc

Bill Verburg

You have to remember the your setup is not the same as the op's, you have much more front bias due to the 322mm rotors vs the op's 304mm rotors. Your's are essentially(at least closer too) 964RS/Cup. The Cups eliminated the p/v for track use.

Marc Shaw

Bill - you are correct and the op should take that in to consideration before making any brake bias changes.

Marc

freedman

Digging up an old thread

Is there any benefit to changing the proportioning valve on a C4 running standard brakes bar ugraded pads?

Cheeksyboy

I wouldn't have thought so mate, you're only changing the friction level not the volume/force of fluid being applied to the pad.....

...but someone like the good Dr Alex will doubtless chime in with some proper tech-science stuff

alexjc4

lol for once, I'll admit I have no idea!

Cheeksyboy

Where does that put the rest of us then!?

Isn't the idea that the proportioning valve stops too much pressure going to the rear and thus locking up the rears?

I'd imagine it's a 'safety' factor for the road, hence not required when on track where brake bias/balance is affected by many more variables, whcih you set the car up for on a per track basis anyhow?