996 TT/GT3 4 Pot Calipers

[twoqu]

I know there are a few members considering using the 996TT/GT3 calipers for conversions. Thought it might be an idea to pool resources in one thread.
So if you have any questions or something to contribute put it here.
I'll start the ball rolling with an (amateurish, not mine) illustration of the difference in physical size betwen these calipers and the more popular 996 variant. I belive the centre to centre is 142mm rather than the usual 130mm of other Porsche Brembo calipers.
Obviously there are a few variables to consider namely the wheel size and the brake disc size and whether you want to use an OE disc or something more exotic. Without committing to a disc size it will be impossible to design a bracket.
Having said that there have been brackets, some of which have been RS2 specific and some S2. The RS2 had the advantage of using Porsche discs which of course the S2 does not and I am not familiar with the dimensions.
I have added another dimensional resource. Please note that these really don't help with the critical dimensions needed for brackets but are just for reference to the physical difference. I am not certain but I think the 996 352 425 rear GT3 caliper is dimensionally the same as the 996 351 425 but with smaller pistons.

[twoqu]

Disc size?

Based on what Porsche used and other conversions I have seen, I would suggest that the range is somewhere between 323-350mm in diameter and 30-34mm in width.
Porsche used both a 330X34 and a 350X34 disc using the same caliper and indeed there are conversion spacers to upgrade a 330mm equiped 996 to the 350mm disc.
I have seen other Audi conversions with OE A8/S8 323X30mm, 323X32mm 993TT 2 piece and an OE A8 360X34mm disc that was eventually machined down to 350mm as there was an issue with the pads. There is concern that a 30mm disc is too thin, that the 993TT are too expensive and the 360mm disc too heavy, beside which it would need to be machined down!
Certaintly other companies have used the Porsche discs as a basis for two piece conversions in both sizes. This is advantageous as OE discs have a larger annulus than more conventional aftermarket discs. They are also available by many aftermarket companies.

[Error404]

There are couple of Merc disc options, the centre bore just needs to be machined out by 1mm.
There is a 330x32 and 350x32 from an ML, there is also a 322x32 and a 344x32 from a CLS. The 330x32 option is comparable weight wise to the S8 323x30, so a good option, with better cooling.

I'm working on a setup using these 330x32 discs, with a view to spacing out to use a 350x34 2pcs setup when funds allow.

[Rusty]

Good ideol Robin.

I was looking at 330x32 also, as I want to retain 17" wheels on there. The ML discs seem to be the best bet in terms of dimensions and what's required to fit them.

To retain 17s, 340mm would be as big as I'd dare to go, as some tests with the 996.351.425/6 callipers indicate that they can still fit under my wheels with a 345mm S8 disc. Just.

For 30mm thick discs, I'd retain my 996 Carrera callipers, as there's really nothing wrong with the braking on them; I just want to balance the 314mm discs I have on the rear now I did consider machining some S8 discs down or getting custom bells and 2 piece 335mmx30mm but they're expensive...

[Gazmitchell]

This is an upgrade I'm currently sorting with 996tt calipers. The bracket is deffo the tough bit to find ... And to try to keep the s2 hub is another issue as all the larger and wider ( ie 34mm ) disks seem to be the porsche 130pcd ... Makes your head spin reading all the threads and forums !

[Error404]

There are no commercially available brackets AFAIK, custom is required.
I could get a few sets done and some modded ML discs if there is demand

[twoqu]

I agree! As long as there is a recipe that a few agree on it makes sense not to duplicate effort.
It's the wheels that are the biggest variable. I would think at least 17" to be safe.
Having said that there pics on here of 360mm under 18" S8 Avus and there looked to be plenty of room!

[Gazmitchell]

Tried VRS but no avail and Kev but no go... I've bought a set of custom creation brackets for bembro 996 TT 142 to 94mm but for 100pcd ,so right hole combinations but I'm going to try to mod the brackets to fit 112 pcd ... Thinks it's 17s for me but would love the orig large centre bolt cap to fit as it looks so standard .

[bilko0795]

I have run these calipers now for three years with S8 323x30 Mtec discs and mintex pads and now the pads need changing albeit there is still some life in the pads and also the disc's are fine but have just bought the Merc E330 discs 330x32, but when i went to change them i found that i need a 2mm washer behind the bracket for the calipers to fit over the disc i have also upgraded to Ds2500's pads. Hopeing for less brake dust.

[twoqu]

Tried VRS but no avail and Kev but no go... I've bought a set of custom creation brackets for bembro 996 TT 142 to 94mm but for 100pcd ,so right hole combinations but I'm going to try to mod the brackets to fit 112 pcd ... Thinks it's 17s for me but would love the orig large centre bolt cap to fit as it looks so standard .

What diameter and width are the discs that the brackets are intended for? I have seen some for 334mm for TT etc.
If you can measure from the centre of the mounting holes to the hub carrier to the top of the bracket where the caliper mounts and then from the centre of holes of the caliper mounting to the face where the caliper mounts to the hub carrier, we might be able to tell how far off they might be!

[Gazmitchell]

What diameter and width are the discs that the brackets are intended for? I have seen some for 334mm for TT etc.
If you can measure from the centre of the mounting holes to the hub carrier to the top of the bracket where the caliper mounts and then from the centre of holes of the caliper mounting to the face where the caliper mounts to the hub carrier, we might be able to tell how far off they might be!

Will measure when I get at it it's a work in progress !! Gonna make a start in next few days.. Disc size ideally wanted at least 32 better 34 as jamo on here said that's what the 996 TT are run on ... Looked at merc disks , the q7 vw phaeton and passat w8 think are right pcd but don't want massive dia disks but obviously something to match the pad edge as close as poss. Bit **** about tit as I've not got the wheels I need to see if they'll fit under them ?! Sort of jumped at the 996 TT s then thought about the rest of the set up

[Error404]

Unfortunately brackets are useless without the right disc.
If you can post a pis and some dims of the brackets I will draw them up and see what disc offset you will need

[twoqu]

Agree with Alex!
You either need to stick with the consensus or go it on your own with a bespoke set up. Depends on whether you want the maximum disc within whatever wheel you want to run or accept a solution that will be more than adequate for most mortals.
Looks like Alex solution is quite advanced.

[Error404]

IMHO with good pads, 330x32 will be more than adequate for fast road use and disc weighs similar to the 323x30 S8 disc at around 10.5Kg.
Any larger than that and IMHO you need a 2pcs rotor as the disc weight gets quite silly, almost 13Kg for a 350x32 Merc sinlge piece for example.
For comparison a 355x34 2pcs rotor will come in around 8.5Kg - that will be my "final solution"

[twoqu]

Personally I was looking at making the Porsche discs 2 piece for 2 reasons. The first is dimensionally they are correct. The second is that other reputable companies have used them as a basis for their conversions. Just thought of a third! It would mean that just like the Porsche aftermarket, a spacer would allow running either size with one bracket and caliper and if you were lucky, perhaps even the same wheels. The last is obviously not a factor if you have massive whels to start with!
Unfortunately it would mean two disc/bell combinations.
If as there seems to be 2 Merc discs that only vary in their diameter then the spacer solution would also work. The downside being the increased weight as Alex as said.