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I am using the AP Racing kit for the rear that brings it from 330mm to 350mm with the use of a spacer. Currently on the 350mm AP Racing discs in the front but I have now cracked 2 discs in just 1.5 seasons and its time to make changes.
I don't really want to change out all the calipers, just looking to up size front rotors to achieve better cooling. Considering just picking up a set of used Gt3 calipers if I can make it work.
That’s $4k for a kit that reuses the stock calipers. Kind of pricey. Just get the AP Racing 380mm kit that uses their calipers. A nice feature of those AP calipers is being able to swap pads without removing the caliper. Makes it easy to swap from street to track pads.
That’s $4k for a kit that reuses the stock calipers. Kind of pricey. Just get the AP Racing 380mm kit that uses their calipers. A nice feature of those AP calipers is being able to swap pads without removing the caliper. Makes it easy to swap from street to track pads.
I was just using the RB kit as an example. I am surprised I am not showing other companies offering this upgrade.
Regarding the full AP kit, it brings me to doing the rear as well and I cant justify the 10K upgrade.
Did some research on the topic and got some feedback from various people.
Apparently the GT3 brakes will not bolt up to the standard Carerra. I had someone that did the conversion and found out the hard way. They were told to purchase the Turbo calipers, which do bolt up.
The top is the Turbo Caliper, the Bottom is GT3. You can see the spacing on the GT3 is much wider.
Below is the S caliper. Note the spacing.
I was looking around on ebay for Turbo calipers, came across this listing. It's a set of PCCB calipers and pads, I noticed it includes an adapter bracket.
Looks like this bracket allows you to go from the narrow to the wider spacing caliper mount setup.
The bracket goes under part number:
99735150504 (now under 9P1611315)
interesting that it has a 997 part number. Also interesting when I look it up its for models with ceramic brakes.
So is it possible to run the GT3 calipers with the bracket mentioned above on the Carrera, S, and GTS models? havent confirmed it personally but that is where my search took me.
I'd love to get a set of Turbo or GT3 Calipers second hand and run the larger discs.
I am using the AP Racing kit for the rear that brings it from 330mm to 350mm with the use of a spacer. Currently on the 350mm AP Racing discs in the front but I have now cracked 2 discs in just 1.5 seasons and its time to make changes.
I don't really want to change out all the calipers, just looking to up size front rotors to achieve better cooling. Considering just picking up a set of used Gt3 calipers if I can make it work.
Any thoughts?
It sounds like you have exceeded the thermal mass of the 350mm discs. That can happen, particularly on a car with such a high overall performance envelope. Assuming your car has been modified, more horsepower than stock, R compound tires, etc. all contribute to greater abuse on the brakes. Sometimes, certain drivers are simply harder on brakes than others as well. If you're cracking our AP Racing J Hook discs, any other disc of similar size is going to have even more problems on your car since the AP J Hooks have proven to be the most durable option on the market. You are on the correct path in seeking greater thermal mass. Sometimes that is the only route forward.
Also, are you being careful not to thermally shock your discs? That means you are properly bringing them up to full temperature at the beginning of each track session, and giving them a proper cool-down during each session. Brakes should be treated like race tires in that regard. If you go out and bomb on the discs full blast as you exit the pits, your propensity to crack the discs will go through the roof. Radical temperature swings from cool to very hot and back are what cracks discs. That's why cracked discs occur much more often on tracks with very long straights followed by sharp turns (Watkins Glen, Road America, etc.). Tracks with flowing turns and shorter straights are far easier on brakes (Roebling Road, Willow Springs, etc.). In these cases the brakes may reach a high temperature, but they stay closer to the same temp and aren't seeing the huge deltas in temps that are seen on tracks with long straights...where they are being blasted with cooling air down that straight, and then instantly raised a to a huge temperature when you're standing on the brakes. Please see my comments on thermal shock in the video below at the 2:41 mark.
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'09 Carrera 2S, '08 Boxster LE (orange), '91 Acura NSX, Tesla Model 3 Performance, Fiesta ST
Jeff Ritter
Mgr. High Performance Division, Essex Parts Services Essex Designed AP Racing Radi-CAL Competition Brake Kits & 2-piece J Hook Discs Ferodo Racing Brake Pads Spiegler Stainless Steel Brake Lines
704-824-6030 jeff.ritter@essexparts.com
Yes I just replaced the discs back in April. Got about 8 days on them. I was SUPER careful letting them warm up and cool down after each session thinking I would be able to push these longer than previous set (14 days until one front disc cracked)
Regarding the full AP kit, it brings me to doing the rear as well and I cant justify the 10K upgrade.
We have many clients who upgrade to a full front brake kit while leaving the rear on the OEM size, or running it with our 2-piece rear disc upgrade. This is possible because our front brake systems very closely mimic the OEM brake torque on each axle. Caliper piston size and disc effective radius (diameter or distance the pistons sit from the hub) are two of the factors that influence overall brake torque. If we produce a kit for a car with a considerably larger disc, we offset that disc increase with a reduction in caliper piston size to maintain proper brake torque output on that axle. When you swap OEM parts from one trim level to another, that is not the case. Even if the parts physically bolt onto the car, that does not mean the brake bias is going to be correct. That means you can run into a host of problems. The most notable would be poor integration with the ABS and stability control, and potentially lengthening stopping distances rather than shortening them.
Unless you are struggling with rear brake problems (cracking rear discs and burning up rear pads), and you want a $5k upgrade, you'd be far better off mating our front CP9562/380mm brake kit to your existing rear AP disc upgrade. You can see the kit here: https://www.essexparts.com/ap-racing...mm-porsche-911
This kit features an incredibly stout 380x36mm, 72 vane AP Racing J Hook. This disc is going to be far more effective and efficient than an OEM 991 GT3 front disc. That kit also uses a high volume pad that will last a long time. It also comes in red or black depending on what color your stock rear calipers are (I'm assuming they are red). So visually it will integrate nicely with your OEM rear calipers.
Keep in mind that even though a 911 has more balanced front-to-rear brake abuse than something like a Corvette or Camaro, the front brakes still take far more abuse than the rears. You'll be better served by going with the best front system possible, rather than kludging together a bunch of mismatched parts from other vehicles/trim levels. Our system will provide you with a setup that eclipses the 991 GT3 (or Turbo) front brake system performance. Our system comes in one box, you don't have to search around and buy a bunch of parts from different vendors and hope they all go together on the car properly. Our kit even comes with a set of Ferodo DS2500 pads and fits behind C2S wheels without a spacer. Piecing together parts from other trim levels can be a recipe for poor integration, poor performance, lots of wasted time, and no support system if you run into any problems.
Below are several reviews of our 380mm system for the 991. We have a whole bunch of happy 991 and 991 owners running this system. Many of them are running it at both ends, but some are running it just on the front as I'm suggesting.
Yes I just replaced the discs back in April. Got about 8 days on them. I was SUPER careful letting them warm up and cool down after each session thinking I would be able to push these longer than previous set (14 days until one front disc cracked)
Understood. It sounds like you are just pouring too much heat for a disc of that size to handle. It can and does happen. That's why our entire range of upgrade options exists. We have bigger solutions if you need them. A couple other questions:
What pads are you running front and rear?
I'm assuming you don't have any type of aftermarket brake ducts installed?
Have you removed the dust shields behind the discs?
What tires are you running?
Understood. It sounds like you are just pouring too much heat for a disc of that size to handle. It can and does happen. That's why our entire range of upgrade options exists. We have bigger solutions if you need them. A couple other questions:
What pads are you running front and rear?
I'm assuming you don't have any type of aftermarket brake ducts installed?
Have you removed the dust shields behind the discs?
What tires are you running?
Thanks!
Running AR-1 tires, and front and rear DS3.12.
The rear AP 350mm kit I have look pretty good. Has over 20 days on it. Its thinning out but no serious heat cracks or anything.
No extra ducting installed and my rear rotor covers are removed, thanks to your feedback when I was installing the 350mm front and rear AP disc upgrade kit.
The rear AP 350mm kit I have look pretty good. Has over 20 days on it. Its thinning out but no serious heat cracks or anything.
No extra ducting installed and my rear rotor covers are removed, thanks to your feedback when I was installing the 350mm front and rear AP disc upgrade kit.
I am pushing the limits of the system, I get it
Good, good. What horsepower are you at, and what tracks are you running?
07-23-2022, 08:13 AM
991.2 S Brakes to 380mm Discs
