greenr

Is there a difference between the calipers on a 1991 C4 and an RSA? Can I use the RSA calipers on a C4 or do I need to start replacing rotors and pads, etc.? Would it be better to upgrade to a 993 brake set up? The car is a daily (some spirited canyons) and sees ZERO track time. I have read the posts and am getting confused about size and bias so simple guidance would be greatly appreciated.

Thanks!

Bill Verburg

All normal 964(non turbo, non RS...) have the same front calipers and rotors, there were 2 different versions for the rear C4 & late 964 have 4 piston rear calipers early C2 have 2 piston, all have the same rotors

A C4 will have the same brakes front and rear as an RSA 4 piston front and 4 piston rear on 298x28 front and 299x24 rear rotors, pads for the these are the same as was used on 930s(front & rear pads are the same)

The main reasons to change the brakes are
1) better thermal performance for track use - if you aren't boiling the fluid then you don't need more brake
2) looks - this is personal

stock a C4 has a 23.8 mm m/c w/ electro hydraulic boost, pedal ratio is ~34.7 which is good, For sporting use 30 would be better, but still better than the RSA w/ ~46.2

stock torque bias is 1.889/ 3.498 below /above the p/v knee, both are front biased, this is safe. thru '83 all 911 bias was 1.491 w/ a 35.3 peal ratio for boosted and 41.3 for non boosted cars.

993 calipers can be used
in front use the black 993 caliper w/ a 928S4 304x32mm rotor + an aftermarket caliper adaptor, or change to 993 wheel carriers w/o a caliper adapter(bolt on)
in back use a 993 black 4 piston caliper w/ the stock rotor.

If you want holes in the rotors there are other more expensive options w/ the 993 calipers
bias is 1.659/3.071 still front biased but not as much as stock

A bigger set is either 993 or 993RS calipers on 322x32 rotors
the rotors here are 928GTS w/ either caliper and a caliper adapter

again for holey rotors there are other ways to go

unfortunately the 964 hasn't got a bigger rear option w/o giving up the parking brake
so bias w/ the 322 front and 299 rear rotors is 1.659/3.071 or 1.713/3.171 depending on which caliper is used

an option for a better pedal on a C4 is to use the 964RS 25.4mm m/c

Matt Andrews

Do you write that every time you post it Bill? Or do you cut and paste?

I really appreciate your through responses to brake questions. Thanks for continuing to post them.

John McM

Standard C4 calipers and discs with suitable pads and a good fluid (fresh and high wet boiling point) should be all you'll ever need. This is a Porsche not a Toyota. The factory anticipated this type of use.

Marine Blue