The piston sizes are the same between the red and yellow 997.2 GT3 calipers, front and rear. On the front 997.2 Turbo PCCB calipers, the pistons are larger compared to the 997.2 GT3 fronts. As a result, the 997.2 GT3 calipers will give you a harder pedal compared to the TT calipers and they will also shift the brake bias to the rear. Unlike the GT3 calipers, Porsche does NOT sell a rebuild kit for the odd TT piston sizes. I would not purchase the TT versions..

 

I have a 2009 Turbo (997.1) with PCCBs so what calipers do I have?

 

You have the yellow 997.2 PCCB calipers with 380 front rotors. These calipers have 28/32/36mm pistons. The 997.2 GT3/Cup 380 calipers have 28/30/32mm pistons. Visually the TT and GT3 calipers are the same but the piston sizes are different. The old style 996/97 GT3/TT 6 piston calipers used with 350mm rotors have 28/32/38mm pistons.

 

Porsche is aware of more front axle weight of turbo vs gt3 so it is very logical for TT calipers to have larger pistons...I really wonder why you suggest to a TT car to install gt3 calipers (front) that are designed for less axle weight...

 

The GT3 calipers will give you a harder pedal which is preferable if you are tracking your car. I have run both versions on the same car and it's noticeable. The GT3 calipers will shift the brake bias slightly to the rear which helps the car rotate under trail braking. It actually gives you the impression that the brakes work better as you have a shaper bite point. The GT3 versions are also easily rebuildable because you can purchase complete caliper rebuild kit from PMNA as the GT3 piston sizes are identical to the Cup calipers. There is no such kit offered for the TT caliper so the only option is to source aftermarket parts or buy a whole new caliper. That almost happened to me as several of the ceramic piston insulators cracked on a set of 6 month old 997.2 TT calipers, and NOBODY sells the insulators, not even Brembo. Luckily Porsche took the pair back under warranty but had they not I would have had a couple of expensive paper weights. If you drive your car hard or track it, NOT being able to rebuild a caliper is a huge drawback. I am not telling anyone to purchase the GT3 versions over the TT ones. People can do what they want. I am just saying that I would not buy the TT versions. I have tested both and personally prefer the GT3 version for the above listed reasons.

Compared to a GT3, the TT is a heavier car but the weight distribution is similar for both cars as the TT is heavier on both ends, mainly the front drive in the front but also the turbos, ICs, rear seats, etc, in the rear. You can also alter or fine tune brake bias through pad compound selection so small differences is weight distribution are negligible. Plus, the minute you alter your car by removing weight (as many do), or modify your suspension with different spring rates, dampener, sway bars, tire sizes, and other items, everything is out the window anyway as far as the effect of the factory brake bias is concerned on the balance of the car anyway.

Finally, Porsche offers the 997TT with 350/350 steel brakes or with the optional 380/350 ceramic brakes. All other components like the MC or ABS module are the same but the brake bias will clearly be slightly different for the two systems.

 

I really respect and admire your knowledge regarding porsche caliper details...however by replacing front calipers of a system with calipers having smaller diameter pistons you just minimize braking force applied to front wheels.and so the car becomes rear wheel brake biased...this is not the correct way to adjust brake bias between axles...total braking power of a car needed to stop from certain speed is always the same for same weight regardless brake biasing...so when you remove braking power from front axle you simply add it to rear brakes...resulting in possible overheating of rear brakes and premature failure or rear pccb disks...as an engineer I would think of the best way to rear brake bias a turbo is to replace rear calipers with ones with larger diameter...thus front braking power stays the same but rear end brakes more powerful...I would really like your opinion on that...have you ever tried such a solution?

 

So I guess there's no way to get the factory red calipers for 380mm rotors without affecting the brake bias?

Are the rear calipers the same?

 

You say this is not the correct way to adjust brake bias between axles. I don't know. Tell that to Porsche because this is exactly what they did with the 997GT cars. The 997GT2/3 runs the same exact brake master cylinder as the 997TT. Brake rotor diameter of 380/350 is the same. The major difference Porsche did was to reduce the front piston sizes to "slightly" shift the brake bias toward the rear of the car. Why did they do it this way as opposed to larger rear rotors? Probably economics. Why did they do it at all? Probably because through track testing they found out that by shifting the brake bias slightly to the rear they were able to actually improve stopping distances because the rear brakes were now utilized more.

Yes, since the rear brakes are utilized more they will naturally run a little hotter but the majority of the heat is induced when guys run at the track with PSM "ON". You do that and you will drastically reduce the life of the rear rotors in as they will run several hundred degrees hotter. I've seen it plenty on 997GT3s and TTs. Rear calipers start to turn from yellow to orange while the fronts still look like new. I always take tire and brake rotor temperatures at the end of each run at the track to monitor everything. Most accomplished drivers will start their car and immediately turn off the nannies. For street driven cars, shifting the bias slightly rear is a non event. You just don't put that much heat into the system to have any impact. If you can manage to overheat the brakes on the street, you are driving like a maniac.

No, I have not tried larger rear rotors. I really don't want to move away from what Porsche has determined to work optimally on the track. There is not much you can improve on the 997GT3 380/350 brakes. They are good.

Finally, what do you think the brake bias is like on the 997TT that has 350/350 brakes on it compared to the 380/350 set up? I haven't done the math but I bet it has a greater rear bias than the 380/350 set up since the 380s will provide a greater braking torgue due to the larger diameter. Obviously Porsche has determined this to be a non issue.

 

The only factory red 997.2 380 calipers are the 997GT3 and 997 Cup versions used with steel 380 rotors. The rear calipers are all the same...

 

You seem like a guy that has excellent knowledge of porsche cars....and that makes me wonder why you dont even care to mention that 997tt and 997gt2 or gt3 have different weights...porsche installed larger pistons in 997tt because is heavier in front end at absolute value and due to the fact e=(1÷2) musquared more braking power is needed to stop thecar compared to gt2 or gt3...2 wd gt cars dont have front diff with shafts and so they weigh less...that is why porsche installed smaller diameter caliper pistons in gt3....there was no need for the larger more powerfull turbo caliper pistons...I believe the answer is so simple...
Apart from this since you like to rear bias your brakes by removing power from front calipers....its your car my friend....maybe a 100-0 mph brake test might convince you you lost a part of 997tt pccb excellent braking power....

 

Also regarding your last comment between 350/350 and 380/350 disks...remember you said that steel 350 front calipers arethe same with pccb 996 calipers and are slightly larger in pistondiameter than 380 pccb calipers...maybe thats the way porsche achieved more power compared to 997tt pccb with 380 and smaller pistons...what do you think?

 

If you look at post #35 you will see that I did talk about the weight difference between the cars. Stick two fat buys in a GT2 or one skinny driver in a TT and both will weight the same. This weight comparison relative to brake output is negligible. Just like most people on this forum however, my car is not stock. My car is RWD, no PSM and weights just over 3200 lbs. It is a 90% track car. I am stating what system I use and why I prefer it. I have run both set ups. Have you? I felt like my braking improved with the GT3 calipers as the rear was able to contribute more. That is my experience in my application. As I have stated previously, people can install or modify their cars how they see fit. I am not here to win an argument or persuade someone. I don't care if you remove the brakes from your car altogether and stick your foot out the door braking like Fred Flintstone. All I'm saying it that obviously Porsche finds it acceptable to run a 380/350 and 350/350 system on the same exact cars, so this whole hair splitting of brake bias is pure semantics. It doesn't take a rocket scientist to realize that the 380/350 brakes are more effective than the 350/350s. How is it possible that Porsche would allow that on the same car? Obviously because they know that the 350/350 brakes are more than sufficient with the 380/350 pretty much overkill for the street. In the end, do what works for you and makes you happy...

 

Yes, one of the pistons in the old style 350 calipers is 2mm larger than the 380 TT calipers. Based on what I have seen, I don't think that is enough to offset the reduce leverage of the the 30mm smaller rotor but you could argue that till that cows come home. I ran my car with the 997.1 350 calipers, 997.2TT 380 calipers, and 997.2GT3 380 calipers. I felt that the 997.2 TT calipers had the greatest amount of front bias as ABS in the front was easiest to invoke of the 3 set ups. It wasn't a huge difference but enough to be noticeable. The bias of the 997.1 350 and 997.2 380 felt very similar, pretty much a toss up which leads me to believe that the 997.1 350 and 997.2 GT3 380 front have very similar brake output. Again, don't take this as gospel, this is just my observation running the 3 set ups on the same track. YMMV. The rear calipers were all the same, btw.

 

Now we are talking....Johnny db has a 4wd 997tt and I am sure he doesnt wish to minimize brake power applied by his pccb calipers....however since your car is rwd I agree with you installing calipers porsche designed for 2wd cars....after all I really enjoy a thread with respected opinions like yours...

 

Bumping this old thread

So has anybody tried this? I have a set of PCCB rotors that i would like to use with my non PCCB calipers 997.1tt.