Bill Verburg

Adrian

The old cup car stuff is coming in again. The 964 Carrera Cup did not have a bias valve, nor did it have ABS. This is a race car. Off the top of my head the Carrera RS had a proportioning value of 0.36.
None of this has anything to do with installing larger brake systems on a C4.
Each model of 964 has to be approached differently and based on a large number of variables set up exclusively for that 964.
There is sufficient practical data around from people who have actually done this work which shows up the pitfalls and what has to be done for a specific model.
The Carrera Cup which is a race car is not yet again the standard or the example to use when trying to set up a C4. The use of some Carrera RS parts is not to duplicate the braking system of the RS but to overcome shortfalls in the C4 or C2 braking system which may occur when installing bigger brake systems. The RS MC for instance will provide a little more brake fluid capacity and will provide courtesy of its slightly larger piston diameter a tad more brake pressure. For the C4 only of course in this case. This MC cannot be used on a C2 with its vacuum boost.
The beauty of this thread has been that it has shown to all who read it that just slapping on bigger brakes and suddenly you can stop faster is a myth and that many issues have to be researched first.
Ciao,
Adrian
964C4

tonytaylor

Adrian

Completely agree; if you want to stop faster than the stock system you`ll need stickier tyres for a start.
On a C2 I found that the big brake conversion made braking worse (although they were less prone to fade due to better ablity to withstand heat) until the larger master cylinder was fitted.

Adrian

Dear Tony,
I have been doing this on rennlist now for nearly five years. From day one the first advice I ever offered when people asked "how to improve braking" I would always answer, purchase a decent set of tyres suited for the job. I have seen people spend $US10,000 on brakes and suspension mods and then slap on the cheapest and widest set of rubber they could find. Then they complain that the mods do not do anything. Very sad but very true. Sometimes I think some people get blinded by the red and forget the black.
Ciao,
Adrian
964C4

Bill Verburg

Cupcar will need to confirm but according to my records the Carrera RS(euro not RSA) and Carrera Cup cars(all) used the large 44/36 on 322x32 & small 34/30 on 299x24 w. a hyd boosted 25.4mm m/c w/ a 55 bar knee(.46) p/v and a special ABS unit

Yes, bigger tires stop a car more quickly but that is not the issue here. Terry(C4guy) reported thermal problems due to dual drivers at DEs. The first thing that should have been done is the usual ducting/fluid/pad upgrades. After that the next step to cure thermal issues is bigger rotors.

The 322x22 rotor used w/ the Big Red is certainly a good choice.

The issue has become is it necessary to change m/c? My opinion, based on personal experience w/ my car and comparable factory setups) is that the existing 23.81 is more than adequate.

and do the rear calipers need updating? My opinion is yes, to retain bias, but it is something that can be done in steps. try the Big Red fronts w/ stock rear carefully, keeping in mind the bias has gone very forward, I would eliminate the p/v as it only moves bias more forward. If this setup is less than satisfactory(I believe that it will be) then the solution is a pair of 993 small 34/30 rear calipers on your existing rotors(or the same size 968 sport rotors)

BrokeAss

Bill, Adrian and everyone else....
That you very much for sharing your experience! This has thread has been very educational and very helpful. I now have a clear roadmap of the steps that I'm going to take going forward and my eyes are opened to the tradeoffs that will result.

- Big Sticky Tires - check - We track the car with Kuhmo Victoracers.
- High Temp Fluid - check - I'm using ATE Super Blue, and I bleed regularly. (also completely flush the system annually at the shop using the Bosch Hammer to open the ABS valves)
- Pagid Orange pads front & rear are one their way!
- I'll install the Big Red kit up front, leave the stock rotors & calipers in the rear and use the Pagid Orange for track events. I know this will leave me with a forward bias.
- I haven't ordered any brake ducting yet. I've been disappointed that most of the fog lamp replacement kits only duct air as far as the fender liner and don't duct the air directly into the brake backing plate. That being said, I suppose some additional airflow is better than none at all.

Hopefully this investment will let my wife and I focus on DRIVING at Sebring and so we won't have to worry about cooking the brakes!

After trying Sebring with this setup, I'll scrounge under the sofa coushins and get some funds to change the rear rotor/calipers as Bill has recommends.

Look for a big post-Sebring report around September 22!

Thanks again!

Bill Verburg

Terry, any air ducted in is better than none and it is important. There is a natural flow from inboard to outboard, anything that lowers the inboard temps will help.

Another cheap and easy addition to ducting are these 993 scoops which attach to the control arms.


This is a 993 w/ ducts and scoops

Bill Gregory

964's already have those scoops as standard equipment.

Bill Gregory

Another option, staying with Porsche parts, is to install the Turbo 60 bar bias valve, which gives additiona rear bias (I agree with Bill that with big reds in front, removal may be a good choice). Of course an adjustable bias valve, or complete removal as mentioned, are options.

JC in NY

I believe we have gone through this already. The Euro Carrera Cup race car uses the standard ABS, not a special racing unit. Cupcar I think can support this. The 964 that used a "racing" ABS was the RSR.

Bill Verburg

Thanks John, My mind is like a sieve, and getteing worse daily

Yes, an adjustable p/v will certainly provide more options.

Adrian

My apologise on the 0.36 it is 0.46. The numbers 36 are in my head because the hydraulic boost ratio for the Carrera RS is 3.6:1 against the rest which are 4.8:1. I knew there was a 36 in there somewhere.
Ciao,
Adrian
964C4

PS: The Carrera RS NGT was not fitted with ABS. The mounting bracket is removed as part of the seam welding process. On the RS basic and RS touring the bracket is reinforced. I can confirm the RSR has a special ABS system installed because I have special photos of it. It was required to be disabled though for different race series. The Carrera Cups I have seen from 1990 to 1994 had the ABS removed. I do not recall a bracket either. Next time I am down at Brunos I will take a peek at one of his.

Bill Verburg

If I were lucky enough to have a Carrara Cup, I would likely remove the p/v as well. They have the medium 44/36 calipers on big rotors and small 34/30 calipers on small rotors. The hyd bias is the basic 1.6 always used on 911 but the mechanical bias has been moved considerably to the front. No need to move it further w/ a p/v

Adrian

I hope that everyone realises that there were actually different versions of Carrera Cups. There was the Porsche Carrera Cup used in the Carrera Cup series and there was the Porsche Carrera Cup used in the Pirelli Cup series which by the way is still run in Austria. They were also raced in the German ADAC GT Cup series.
Versions of the Carrera Cup were also modified to run at LeMans. These were called Porsche Carrera Cup Mod. One of the teams that ran these machines was the ECURIE team in 1993 and 1994.
What is the point of this post. Simple. What example does one use when quoting data. The fact there were different Cup versions for different series with different rules shows that nothing is quite that easy. Nor is it with Carrera 4s or 2s. You have a number of different versions, combined with POs modifications and the list goes on. Research, research, research are the three key words.
Terry, a lot of which I told you in my email answer to yours yesterday has been repeated by the two Bills here. Nice to see that we are all in basic agreement.
Ciao,
Adrian
964C4

JC in NY

I think when most people refer to Cup cars they are referring to the Porsche Carrera Cups (and Supercups) and not the GT cars which may run in a series with the word "Cup" in the name, like ADAC Cup. The GT cars are totally different. Cup cars are well ... Cup cars.