Another 996 calipers on SC question

[SFR]

Hi all - I’ve read a lot about this about 3 month’s ago and rather than go back to confirm what I need, please help.

I don’t t have any brakes so everything needs to be purchased; I’d like to go with 996 (if only for the look).

I’m planning on buying front and rear 996 calipers and the adapters from, I guess, Elephant.

Question, the rotors - can I use the 996 front and rear rotors?

If not what car would these need to be from?

My car is a 1980.

Thank you

[2.7RS]

You can't use 996 rotors on your SC conversion.

When I did mine years ago on a track car pretty sure I used Carrera rotors (84-89)

The other issue I had was brake lines. I got those made at a hydraulic shop

[SFR]

2.7RS - thanks for the input, but now I’m totally confused.

I thought these adapters were for putting 996 calipers on a SC??

https://www.pelicanparts.com/More_Info/STOMSKISR039.htm?pn=STOMSKI-SR039&gclid=Cj0KCQjw48OaBhDWARIsAMd966BdHviwDXJNDsDjzEG7 m6CgrQinr19MTUpD2H-qhVR2WQh8iUonMloaAgqgEALw_wcB

[darrin]

SFR, you can mount the 996 front calipers but will then need to run them with rotors specific to your car (Carrera rotors will fit your SC). Be sure you understand/address any front to rear brake bias/proportioning differences between the brakes stock to your SC and the 996 -- I know that some of these conversions can significantly change this and create unforeseen issues.

[spuggy]

Originally Posted by SFR

Hi all - I’ve read a lot about this about 3 month’s ago and rather than go back to confirm what I need, please help.

I don’t t have any brakes so everything needs to be purchased; I’d like to go with 996 (if only for the look).

I’m planning on buying front and rear 996 calipers and the adapters from, I guess, Elephant.

Question, the rotors - can I use the 996 front and rear rotors?

If not what car would these need to be from?

My car is a 1980.

Thank you

TL;DR - I'd suggest you upgrade the front to 3.2 rotors/calipers and either stick with SC for the rear (if you have them) or fit 3.2 there as well and call it good.

Boxster calipers != 996 calipers.

Boxster S calipers are the same calipers (except for color) as 996.

The Elephant kit to use Boxster calipers doesn't use 996 (or Boxster) rotors, it takes 3.2 rotors (84-89) front/rear. So with an SC you'll need to source/fit those.

Boxster, Boxster S/996 and 996TT calipers all have the same piston sizes - IMO you should use a 930 M/C. If you don't, I'd expect a squashy pedal with lots of travel instead of a high, firm pedal.

The Boxster kit may give improvements in pedal feel/modulation with the correct M/C, likely the calipers are stiffer (although the adapters don't help here). The calipers may be lighter. Oh, and they look better. But the issue with 3.2 brakes is the lack of thermal capacity due to the comparatively thin rotors, which won't be helped by the higher clamping forces/bigger piston areas in the Monoblocs.

So you'd be using a setup capable of generating more heat with rotors that already have known issues with heat dissipation under hard usage with the factory calipers.

The parts came from an ABS car, a system you obviously don't have in an SC. It'll be considerably more front-biased than the factory ratio, which can only be addressed to a certain (small) extent by "grippier" pads in the rear. You'll still tend to push the fronts when weight transfer is towards the rear, and braking approaching the limit will not be not well-balanced - as the fronts will lock up first. So there's braking left on the table.

Ideally, an SC/RS pedal box or a Fabcar dual-master to address the bias. As an tandem/in-line dual master cylinder with appropriate, dissimilar, bore sizes to use with the booster doesn't seem to exist (I'd love to be wrong, someone give me a part #! ).

You may be thinking of the Instant-G 996 (or 996TT) conversion, which does use the 996 (or 996TT, depending - to suit the calipers) rotors, and comes with modified hubs to accept them.

You'll need 17" wheels to clear 996 calipers over 996 rotors. 996 calipers are very tight on the inner spokes of my Ruf Classics, TT calipers almost certainly would require spacers - or different wheels (winter wheels are G-model offset Cup 1 clones, and they have masses of clearance).

There are comparable front bias issues with 996 as Boxster, and 996TT would have even worse ratio (but not quite as bad as 993TT).

The Instant-G hub arrangement does seem to move the wheel inboard slightly (I'll SWAG 10mm), so my 225/45/17 has a little more clearance on the (rolled) fender lip now.

You'll need to go to the track to gas off any new pads, as 500 miles of trying on the road simply won't ever get the brakes hot enough. At least that'll be it for the next 10 years or so, because the pads & rotors just don't seem to wear...

If I were to do it over, I'd probably use the Elephant 930-ERX setup with a late servo now.

[Bill Verburg]

996 calipers are the same as Boxster S calipers and use bigger rotors than Boxster

Boxsters are designed for 298x24mm f and 292x20 r, stock '84 Ca-89 Carrera 3.2 fronts are close enough and stock SC rears are also close enough there


Boxster S and 996 want 318x28f and 299 x24 r rotors, Instant G is the only one that I have seen do a close to decent job mounting the 996 rotors on a 911

Here are the brake torques and bias of several brake setups that I've used on 911s

The best 2 are the far left,stock thru '83 911 and the 993RS on the far right, Boxster are the Salmon tops in the middle, yes too much front and it adds to the only issue w/ stock brakes which is thermal overload on the front in repeated hard brakes(AKA track use)

The additional torque available from other than stock A & M is only useful when tires and aero have been significantly upgraded


for track use you want to upgrade the thermal performance envelope
here are the relative thermal capacity of ll the easily fitted bolt on to stock hubs rotors


Any of the upgrade calipers except wide A f will want a 930 m/c

[SFR]

Spuggly, Bill - thanks for the information.

I did look at the 930-ERX kit, its $6,800.
With the engineering/modification Elephant did to make it a bolt on kit - I’m sure it’s worth it, however, unfortunately not in the budget for this build.

I’m hoping to be able to put tougher a ‘good looking’ and functional kit for less, 17” wheel are fine.

[broncozx]

https://www.rsrproducts.com/product-page/rebel-s-racing-996-boxter-s-to-911-front-caliper-adapter-kit

[broncozx]

rsrproducts.com

[H-viken]

Bill, just out of curiosity, would running a “square” set of wheels on a narrow body (for ex 7” all around) mitigate some of the unbalance towards the front that’s generated by the Boxster brakes?

Johan

[Bill Verburg]

Originally Posted by H-viken

Bill, just out of curiosity, would running a “square” set of wheels on a narrow body (for ex 7” all around) mitigate some of the unbalance towards the front that’s generated by the Boxster brakes?

Johan

No

The whole purpose of bias is

1. safety, if something is going to lock have the fronts lock first
2. offload as much of the thermal load from the front to the less stressed rear as possible
3. involve the rear in actually stopping the car as much as possible

having a square setup will not really affect at least the 1st 2 items

[H-viken]

Got it, thanks Bill

[Peter Bull]

Spuggy and Bill Verburg have covered the most important issues, so I just wanted to add that if I had to do it again I would do the Instant-G 996 brake upgrade again.

In addition to the kit from Instant-G, I got a set of used 996 calipers from eBay, rotors and 930 brake master cylinder from my favorite parts dealer, and a set of Performance Friction pads.

I've had the kit for quite a few years, the car has seen street, auto cross and track use. And some abuse, purely for research. The brakes behave well, and I've never had any lock up problems.

/Peter