fbfisher

You have 20 minute canyon runs over there?

Cupcar

One thing to keep in mind is that the front to rear brake distribution is dependent on changing factors such as fuel load weight or the tires going "off" in addition to the factors surrounding the brake components themselves.

The best solution is an adjustable mechanism for a race car. Note that the latest SuperCup and RSR cars come from the factory with a dual master cylinder and whiffle tree set up controlled by a good ol' Tilton **** from Buellton California in the dash. No ABS for them either.

Another solution would be an adjustable proportioning valve such as the Tilton or Wilwood in the drivers compartment.

Bill Verburg

This is how the factory did it on the 964 L/W
Cockpit mounted bias valve


Triple m/c


triple reservoirs

Cupcar

Cool, I also note an extra wide brake pedal on the Lightweight

Interesting that they used a dual master cylinder that has a basic adjustment and the proportioning valve in the rear for touch up changes on the track back then.

Here are some Tilton proporting valve options to do the same:



It is available as a **** or a lever type, the body is around 1.25" long, click on link below for more information.

Screw Type Valve

Lever Type Valve

These valves have a turnover point that is adjustable from 0 to 70 bar and it looks like the metric unit may be a direct replacement for the Porsche valve since it is not much longer than the factory unit.

This would give you a very nice adjustment potential as you would have the equivalent of all the Porsche valves in one unit and then some- particularly if installed in the cockpit. Could be a cool project!!!

Cupcar

By the way, here is the adjuster kit the factory uses in the new RSR from Tilton, in case you want to install a dual adjustable master cylinder and look 'factory"

Bill Gregory

Earlier in this thread, there's a reference to a two part article on brakes, which focused on brake theory and application, illustrated by the 964 braking system, which was in the June and July Porsche Panorama, published by PCA. For those that don't get the Panorama in the US or for those outside the US, I've uploaded it to the web. Note, the diagram of the abs system is a poor scan, as a placeholder, from a prior Pano article. The original artwork, however, was used when the article was published.

The 2.4mb article, in Word .doc format, is located here. Note there are two embedded tables towards the end of the article. If you're scanning through the document and you come to a blank space, wait a few seconds and the tables will catch up.

Flying Finn

Bill,

Thanks. I actually have that Panorama too but having extra article on computer doesn't hurt!

Martin S.

Thanks to Super Moderator Bill, CupCar and others, readers are getting some really great information on this string. Thanks guys!

kmatts

one of the best posts i have read on RennList in ages....thanks so much. K.

Martin S.

Another great articlle on brakes and how they work in the Real World, is available in the current issue of Grassroots Motorsports. The whys and hows of bedding in brake pads is discussed and I guarantee that most of us will learn something new from this article. I know I did. Let's see if CupCar agrees!!!

This monthly magazine has excellent articles on all sorts of car prep and every type of car racing on a regular basis, + it is a source for little speed secrets that you don't have to tell your frineds, whoops! The secret is out now!

Go up on their web site and get a free issue.

I receive no compensation for my mention of the Grassroots Motorsports Magazine. Note: I have been a subscriber for years.

ToSi

another old thread bump -

Can anyone w/ RS calipers + the base C2 23.8mm master cylinder comment on pedal feel & height vs. the base 993 brakes? How much dead travel was added?

Bill Verburg

You'll have slightly more pedal travel w/ RS brakes, but for H&T you will still need a built up and wider gas pedal

certz

I have driven with the TT-front/RS-rear setup and with stock (and the stock C2 MC) on the track. In my car there is much less pedal travel with the TT/RS setup and the pedal is firmer right at the top. This can make heel-toe a little harder but I got used to it.

Bill Verburg

Unfortunately the laws of Physics not being 'general guidlines' this is not possible

the fornt caliper hydaulics on all 993 are the same, they all have 36/44 front pistons

in back, listed from the least to most hydaulicly demanding calipers

993tt uses 28/28
normal uses 30/34
RS uses 30/36

W/ the same m/c the hydraulicly smallest rear caliper will have the highest and hardest pedal w/ the least travel.

oe, the tt and RS uses a larger m/c than normal which increases pedal effort and reduces pedal travel.

so to compare normal to the others one has to look at the slave/master ratios which are in order from least travel to most travel
tt 29.760
normal C4 30.479
RS 33.654
normal C2 37.311
normal C2 w/ stock m/c and RS calipers 38.331

certz

I am not sure what to tell you Bill, but I can assure you that the pedal felt firmer and it took less travel to get the same braking with the TT/RS setup than it does with the stock. If you want to come to Chicago you can drive the NB and the "S" - which now has the TT/RS setup - and it is the same situation. I'm a mechanical engineer and your logic seems sound, but it is not playing out with my cars. Maybe there is the same something wrong with both my cars that is creating this phenomenon. I value your opinions Bill and enjoy your posts so I am not trying to start something, but I can prove what I have written with the two cars in my garage.