Well I tried pming john and haven't heard back but need to tell the guy yes or no here.

So I picked up some 997.2 gt3 cup calipers from a guy for a great price (380/350mm). He also has some slightly used cup rotors that he would sell for super cheap. Rear is no issue, front is the issue.

The hat on the gt3 is 2mm shallower than the tt. Since you have to use adapters to mount the calipers anyway, I see no issue in machining custom adapters with 2mm more offset to use the gt3 rotor offset going forward. Thoughts?

Secondly, has anyone run 380mm rotors up front on a forgestar f14? Or can someone with the 6 piston 350mm calipers measure for me how much space there is? Based on measuring off my cf10 19s they will fit but is. I know the stock twists dont fit over them.

Thanks guys.

 

I think it's the other way around. When you put turbo rotors on gt2/3 uprights you can add a 2mm spacer.

So putting gt3 rotors on turbo uprights would require removing 2mm

 

No I have it right. The turbo hat height is 69.6mm and gt3 is 67.6mm. That would mean the gt3 rotor sits 2mm further out because the gay is shorter

 

I have exactly the same pieces - and have thought about offset adapters too. But I will likely just wait until I go to 2wd and swap to gt3 uprights. Properly machined offset adapters would be the perfect solution for turbo uprights - especially in light of the fact that the OEM 380mm adapters are not cheap. Having a pair made should not cost much more and if you diy... And your choice in rotors goes way up and the price comes down.

All that said, there are a number of guys running around here (Germany) with gt3 rotors on their turbos. Track as well as street (autobahn :-) And that means braking heavily from very high speeds as idiots pull out into the left lane). Nobody has reported anything negative yet. You do need to shorten the pad locating pins on the outside by 2mm and, depending on the pad you use, might need to remove a mm or so for the pad to fit. I am just an@l enough not to want to do this myself, but technically I can not see it causing any harm.

Are you sure you have cup parts? If so, your pistons are slightly smaller on the front calipers than the 7.2 gt3rs'. Don't remember offhand what the sizes are - I can look that up though if no one else comes through. Your 380mm rotors are 7.2 gt3rs. Could you do me a favor and take a pic of the inside of the hat? The guy who sold me mine said they were rear rotors, and they do look like they could take a parking brake. All other hats that I have seen are simply conical inside. But afaik, Porsche never had any 380mm rears on the 997 and the part #'s stamped on them are for the fronts.

 

He's speaking of machining caliper adapters just like the OEM adapters Porsche uses for the 380mm brakes on the turbo - only offset 2mm to the outside.

 

Why would you need to cut down the pins. They are the exact same calipers used in the 997.2 gt3 rs and pccb cars with 380mm rotors up front. Rears are still 350mm. And yes I'm sure they car cup parts. The guy has 3 sets of these which were all extras used on their teams cup cars.
Yep exactly. I'd have to relook but I think the porsche adapters are like 280 for a set so I can easily machine a set for less than that. I could very easily make a few sets if it was something guys wanted both on pot and 997 turbos.

 

I am running 380 mm stoptech's with f10's and no interference.

 

Just sent you a PM Freddy. The Cup rotors may work as they have a slightly deeper offset that GT3 rotors, so they may actually be very similar if not the same as TT offsets. I would not mess around with machining new adapters, just get the proper rotors and sell the cup ones if need be. I would never ever recommend shaving the caliper pins for obvious reason... why would you redneck engineer it when the 7.2 380 calipers will fit a 6TT upright with the OEM Brembo adapter and TT offset rotors?

 

Because if you use the OEM caliper adapters and GT3 rotors on the turbo, the outer pins will contact the rotor - by 2mms or so :-p. I'm talking the bottom pins that keep the pad from sliding down to the inside.

What would those obvious reasons be, John? The increased angular load on the caliper mounting bolts?

I tend to try to look at problems like this logically - not ideologically. Strictly from an engineering point of view, I see no problems with the caliper being offset by 2mm.

All that said, for the 380mm rotors you are not really gaining as much of an advantage by trying to run GT3 rotors. For the 350's, you are increasing your rotor choices exponentially. And that means less expensive rotors are available as well.

The big prob is that there are no factory non-PCCB 380mm rotors in a turbo offset. If you want to go Porsche, the only choice you have is running Cup steel rings on turbo PCCB hats. And that is expensive. And even then the pads rub on the hats on the inside edge. GT3 hats caused the same issues, so the cup teams were shaving the inside edge of the pads (redneck? :-p).

There are only 2 (optimal) solutions for 380mm steel rotors on turbo uprights: running aftermarket rotors or machining offset caliper adapters.

Where did you see this? I would really love to check this and I actually have everything here - except the OEM caliper adapters. The rotors in the style pictured above were avail for the 7.2 GT3RS and for Cup cars. The part #'s are not the same tho, and the Cup rotors have a min. thickness of 30mm stamped on them whereas the GT3RS street rotors have a min. thickness of 32mm. Are the Cup rotors 2mm thinner to start with?

 

Ok I get what pins your talking now. Well if used with a custom adapter that issue would go away.

I think I'm just going to pick up the rotors as see what the measurements are. I k is I can make them work. Cbc machine brackets and be done.

John I'll call ya matse today. I'm sure you're not up and going at 5 unless your working lol.

 

There were a couple of versions of the Cup rotor. I believe this is the latter one for 2011 Cup. I'm not sure if it applies to this version but the early Cup rotor was 2mm thinner, had a deeper offset compared to GT3, and designed for a thicker 19mm pad vs. the standard 17mm pad. The rotor pictured in this thread is also a narrow annulus 63mm rotor vs. 66mm for the street rotor. As such, you must utilize either a Pagid 8003/4 or PFC 7819 Cup specific race pad. I'm not aware of any street pad that is available in the narrow annulus shape, maybe a Brembo pad. Yes, a normal full size pad can be made to fit if you McGyver it and grind down about 4mm of the pad and backing plate. A pain in the **** but can be done. Running race pads on the street does not yield good results and will result in squalling, high rotor wear, and subpar stopping. For this reason alone I would not run Cup rotors but would choose proper off the shelf solutions. Girodisc, AP racing, Brembo make 380s in a wide annulus, 34mm thick rotor for which there are countless number of OEM, street and or race pads available. Giro is the cheapest.

I have run both the narrow and regular annulus 380 rotors. The narrow annulus did not last as long and cracked sooner most likely due to the fact that they have less thermal mass than the wider and thicker rotors. The narrow rotors are marginally lighter at the expense of longevity.

The 350 rotor pictured by the the OP appears to be a PFC direct drive rotor. If it's a rear, it will not work with a parking brake.

 

How could you tell the difference from the pic above? I am seriously impressed! Is it the screws on the hat? My rotors are the street version and have screws around the base of the perimeter of the hat to hold the large aluminum ring inside (What is the deal with that? Do you know? Damper?).

I got my rotors inexpensively enough so that I will run them first. I also have a set of 2 piece 380mm rotors. These are Cup parts. After that I will switch to Girodisc. But I hope not to go through them quite as quickly as you because I am not planning on being on track as often.

And I will be swapping to GT3 uprights.

 

All the cup rotors are narrow annulus. The difference is subtle but clearly evident. I'm not sure how the factory 380 are assembled. The street or cup rotors are 2 piece but not meant to be disassembled unless I'm mistaken. They are not a true floating rotor.

The Giros are good. I got about 50 sessions 12 days out of my last set of 60 vane 380s. They always crack long before any appreciable wear. I normally go through 2-3 sets of rotors and pads per season. The pads actually last almost as long as the rotor so I normally replace the rotors and pads together.