boss302

Hello Guys i need some help. Is there a 355mm rotor out there that will fit/replace the front stock 1987 S-4 rotor so all i have to do is build or buy a 25.5mm or 1" spacer for the caliper.
Do the 993 355mm rotors fit the 928?
Also is there a larger diameter rotor for the rear?

Thanks for any information you guys can supply.

Mongo

Hi and welcome, the original 4 piston braking system is very effective stopping the S4. I have seen big reds (993 Turbo which I THINK is 355mm) on a 928 before, but I don't remember if adapters are required to fit the caliper.

If you are looking to change only the rotor, I don't think it will work properly.

Mongo

I did some digging around and the 993 Turbo uses the 323mm not the 355mm. The latter size is used on the Ferrari F50 and will require new monobloc calipers.

mark kibort

I think i did it the most cost effective way... there is a thread on it

easy upgrade... go to the 322mm GTS rotors and just use some spacers for the stock calipers. you have to radius the edges of the calipers to fit. no structural comprimise. did that for a few years.
Then, the next upgrade could be going to a custom hat and use the 330mm (13") rotor, but generally, the rotors cost $700 (rings) and the hats will cost near $5-700 as well. (i have that now). the main benift for street, is that you go from 322mm to 330mm and a 2 piece rotor for looks. both will function the same.... the GTS rotors will last a lot longer and will perform the same... AND, you need to do more radiusing of the stock calipers to work. both ideas will require simple washers or machined spacers to work. GTS rotors willl require .3" spacers and 2 piece 330mm rotors will require .5" spacers. (very simple).

there other ideas are more expensive.... GTS rotors AND calipers. easy bolt on.
or the 350mm brake kits. new rotors and calipers.

the 993 turbo uses a rotor with a completely different offset and wont work unless you use adapters.

have fun.... the look of the GTS rotor , drilled if you want a more sporty look, is pretty good. the GTS rotor holed, is the exact same part number as the 964T front rotor same offset, identical but cross drilled.

KenRudd

MK-
Do you have any pictures of "radius the edges of the calipers " ?
I was working on a project with Ed S. at Perfex and one of the challenges was as I moved GTS Calipers out on wider rotors, the radius mismatch became more and more of an issue at the edges of the caliper. Sounds like you ran into, and solved, the same issue.

Bigfoot928

I did the Brembo F50 kit upgrade for the front. Direct bolt in. I also did the twin turbo rear upgrade, slight machining to rear mounting point, and then a direct bolt in as well.

buy the right parts and no muss no fuss. Machining a caliper is risky but we all know Kibort defies the laws of gravity and defies the laws of physics when racing.

Unless someone has actually taken a GTS caliper apart and taken pics of before and after machining to show how thin the material is afterwards it is risky.

Rob Edwards

MjRocket

LMAO!!

mark kibort

how much wider were you going with the GTS calipers? I suspect maybe 12.7 stock out to a 14mm?.... that is more than possible by radiusing the outer edges near the same as taking the 12" S4 rotors and making the S4 calipers fit the 12.7" rotors of the GTS.



the part of the "radiusing, its not really structurally compromising the caliper. its outside the bolt, not inside . when I got the S4 caliper out to 13", it was getting very close to edge assembly bolts, but at 12.7" the radiusing was not as much.

mark kibort

here is the additional grinding to make the S4 calipers fit the 13" rotors. like I said, it was very mild to make them fit to the 12.7" rotors 322mmm.
remember we also got scots to work , going from the 11" rotors of the 928 S, to use the cayanne rotors 13" as well. a lot more grinding there!

xschop

What is the S4 caliper dimension from center of Mount holes to center of rotor sweep?

xschop

What is the S4 caliper dimension from center of Mount holes to center of rotor sweep?

Petza914

If you're fitting an S4 caliper, the GTS Big Black caliper will also fit - uses the same mounting and offset. On my '79 I used the adapter kit from 928MS to mount GTS Front and GTS/S4 Rear Calipers. Fronts use a 2-piece slotted Girodisc rotor for a 993TT and I used Black e-coated Powerslot slotted rotors for the rear to have a consistent look. No machining required with the proper adapter kit - just direct bolt-on. Probably need to be running at least 18" wheels to clear the larger GTS calipers.