If I ever went with some bigger brakes in the front, would I be able to move my Bigger front S4 calipers and discs to the back?

88 951S

 

Bigger brakes on a Turbo S?? Spend your money elsewhere for now

 

Im not spending money, im just wondering. These suit me fine.

 

The mounting is different from front to back. I suppose you could get someone to fabricate an adapter for you but it is really not necessary. The rear calipers that you have now are already underused on the car. If you go with, say, Big Reds up front, just switch out the bias valve to a 55/33 to get more braking power out of the rears.

Check out www.944s2.com and see what Tom did.

 

How are the turbo S different than the turbo brake mounting front to back???

 

Turbo S use radially mounted calipers whereas the regular turbo/S2 are axially mounted.

 

So would the kind of caliper adapters I have seen on the market (such as the ones lindsey racing has) solve that?

 

Their adapters would fit, but you likely will need larger diameter rotors as well.

 

yes, assuming larger rotors as well it would work? that is interesting.

 

Try finding bigger rotors for the back, good luck. I've seen some years ago and it's a custom hat and disc. And you lose the parking brake. What happens with just the regular turbo is that some people have moved the front calipers to the rear. All the calipers use the same pad, but the fronts have more braking force from the bigger pistons. You end with more brake torque being applied to the rotor and imminent lockup occurs faster. ABS offsets that but that's not the best way of getting good performance out of your brakes. You should consider selling your front brakes if you upgrade. Like Aribop mentioned, the rears are underutilized as it is.

 

Im talking about using the 928s4 rototrs with s4 calipers, remember? Would there be problems here?

 

That's exactly my point, the problem would be worse. For one, you can't use the front rotors on the rear. Mounting and offset is completely different, and the parking brake won't work at all. The S4 calipers are just too big and too much power for the rear.

 

I see. Now I know! thanks...

 

what are you trying to do - stand the car up on the nose? Bigger brakes than that would be severe over kill and a waste of money.

 

Assuming that you can find an adaptor that will mount a 928S4 caliper to the rear trailing arm and a brake rotor with custom hat to work with the rear internal parking brake assembly (you wont be able to do this w/o having to custom machine a two piece rotor/hat - $$$), marksport is right – its not a good idea.

Look at it this way: the hydraulic force on the pad is the fluid pressure times the piston area. If you use a stock master cylinder after a brake swap, the fluid pressure at the caliper will be the same, since the piston size in the MC has not changed. So the hydraulic force change is just a ratio of the caliper piston areas.

A 928S4 caliper has a 44mm and a 36mm piston per side. I recall a rear Turbo/S2/928 caliper has a 30mm and a 28mm piston. The piston area of each 928 caliper is approx 5076 sq mm, the stock rear caliper is 2646 sq mm. So the 928S4 caliper generates approx twice as much force on the pad/rotor interface – nearly twice the stopping power.

So if you move the 928S4 front caliper to the rear, in order to keep the braking proportion balanced front to rear, you would have to install an absolutely massive front caliper with approx. twice the piston area of a 928S4 caliper (Oooof.)

Otherwise you would need to either significantly reduce the pressure going to the rear, by using a low pressure proportioning valve (aftermarket adjustable bias valve), or going with a custom master cylinder that has a smaller rear brake system piston – but both defeat the whole purpose of installing larger brakes on the back.

The stock car comes with a 18 bar rear proportioning valve. If you want more rear brake, go to the 33 bar. If you install larger front brakes, there are also 45 & 55 bar prop valves available from Porsche. After that, you can remove the prop. valve altogether.

Really no need whatsoever to increase the brakes on a Turbo S for street/DE/autocross use. If you get into building a fully dedicated GT racecar, then you can start exploring ($$) brake options.