briguy

I have a 71 911 t that i'm putting a 2.7 w/ webers. I'm looking into updating my brakes. I realize that I will need to update to SC struts. I've heard carrera rotors with 944 turbo calipers and boxter calipers. Any help would be greatly appreciated.
Thank you,
Brian

Bill Verburg

Best bang for the buck once the 3.5" ear struts are on is 84-89 Carrera rotors and calipers all around. The rotors at 283x24 front and 290x24 rear are 4mm thicker than the rotors currently on your car. Unfortunately the hydralic bias is not ideal with this setup so you either need to use a 33 bar proportioning valve as the factory did or stick with your current M rear caliper and stock rotor(290x20)which will give correct hyd. bias w/o a p/v or try to stretch the old M caliper over the 24mm wide rotors(never done that but heard that some one tried)which will also give good bias.

The main benefit of Boxster or other small Brembo calipers over the Carrera setup is larger pad area. Here is a pic of the Boxster setup;

Notice that it is front only, and uses the same 290x24mm(in this case drilled) rotor as the Carrera.

The small Brembos from 944T,964 etc have a pad area of 172cm^2 for the each end of the car where they are used. The S, A or wide A Carrera caliper has a pad area of 152 cm^2 at the end where it is used. The M, or wide Carrera M has a pad area of 105 cm^2 at the end where it is used. The larger pad area does distribute thermal loads more efficiently. The Boxster caliper is usuallly used with the 24mm rotors so you gain no thermal mass in the rotor only the larger pad area. The small Brembos are usually used with 28 or 24 mm rotors so you do gain some thermal mass in the rotor. The problem with any of the rotors larger than the 24mm Carrera rotors is that they are usually 2 piece designs(in the front) so you now need an adapter for the rotor. Also the small Brembos will need to be machined(for front use) to change them from tranverse to radial mount with a set of caliper adapters also required. Here is a pic of VCIs kit using small Brembos f/r 299x28 mm rotors front, 290x24 rotors rear;

VCI uses a 1 piece rotor in the front but goes to additional trouble by changing the rear from transverse to radial mount and uses an adapter there.

If you are going to all that trouble you might as well use the still larger 304x32mm 930 rotors(2 piece) front and 309x28 mm 930(1 piece) rear rotor. Similar caliper and rotor adaptors are necessary in the front while the 78-89 930 rotor is a direct bolt on in the back. The rear caliper needs relatively minor mods compared to that necessary in the front. Here are some pics of this setup on my car;

rear

front. These are the small Brembos with 930 rotors 304x32 and 309x28. Other pics are at my sites.

The next step up is to use the same rear setup with 322x32 front rotors and either the S4 or Big Red calipers, here is a pic of a Big Red on the 322x32;


There are several other considerations such as master cylinder, stock 19 mm 911 is adequate through the Boxster setup, but after that 23mm is needed. Hydralic bias ratio is critical as there are many variations of piston sizes and possible combinations of calipers, you need to be careful here.

Lastly a set of 930 rotors and calipers can some times be obtained. They present the same difficulties in adapting them to the 911 chassis as the Brembos and are often as expensive or more so than a Brembo setup, in addition they do not use differentialy sized pistons so pad taper can be more of a problem..

AES

Nice post Bill!! Why no 930 pics?

Bill Gregory

Here's 930 brakes on a 911SC, front with VCI slotted rotor:



Rear 930 setup:

kahuna

Bill G,
It looks like the calipers are shaved? Is there a reason?

Bill Gregory

[quote]<strong>It looks like the calipers are shaved? Is there a reason?</strong><hr></blockquote>

In order to fit on the 911SC, the turbo calipers need the fins ground off, which is what you observed.

JackOlsen

To clear Fuchs (7x8x16, at least), you need to either use spacers (1/8-1/4 inch) or shave the fins. For my 930 install, we put spacers in the front, and shaved the fins in the back. The rationale was that the fins help with cooling, so they're needed much more in front than in back (never heard of anyone boiling the rear brakes when the bias is correct).

(Click for a larger picture.)

Front:

<a href="http://members.rennlist.com/jackolsen/FrontRightBrake.jpg" target="_blank"></a>

Rear (this is actually before the outside fins were machined approx 1/8 inch down):

<a href="http://members.rennlist.com/jackolsen/RightRearBrake.jpg" target="_blank"></a>

AES

Thanks Bill, Bill, & Jack. Bill V. awesome car!! I like the new site, good stuff there!

Dave Banazek

For what it's worth you can clear the 930 calipers front and back with 9" Fuchs or with 8" 951 Fuchs.