JRitt@essex

Gents,

You may be aware that our 2-piece AP Racing J Hook Discs are one of the most, if not the most, popular disc choices among 991 GT3 owners. We are currently working on front and rear discs for the both the 991.1 and 991.2. Our discs will work with the OEM calipers, and we will cover all trim levels. The fronts will be 350x34mm, rears will be 350x28mm, and anodized billet spacers will be included to relocate the OEM calipers.

• Championship winning,72 vane, fully-floating, AP Racing J Hook design
• Huge increase in airflow, cooling capacity, and durability vs. OEM and competitor discs
• Saves several lbs. unsprung weight per side vs. OEM iron discs
• Eliminates OEM drilled discs, which are prone to cracking around the drilled holes
• Disc metallurgy specifically designed to handle the temps typically seen on track offer a long service life
• Replacement iron disc rings available at an extremely competitive replacement price
• Anti-knockback/anti-rattle disc attachment hardware
• Available disc burnishing service ensures that your kit arrives ready to be installed and driven hard immediately

They will be extremely similar to these:

Front
https://www.essexparts.com/essex-des...front-997turbo

Rear
https://www.essexparts.com/essex-des...ar997tt-997gt3

Final pricing has not been set, but they will most likely be $1398.00 per pair. While our discs are not the least expensive on the market, they have proven to be by far the most durable. Here's an example of a 991 GT3 customer who got what equates to 70+ track days out of his AP discs!: https://www.essexparts.com/news-blog...g-j-hook-discs

There are lots of other examples of our discs' incredible durabiltity on our blog: https://www.essexparts.com/news-blog

Spare iron rings for our discs are also extremely affordable, and less expensive than some of our competitors.
Spare AP Racing 350x34mm J Hook iron fronts= $349
Spare AP Racing 350x28mm J Hook iron rears= $339










Comparison to OEM discs:








Discs prepared via our burnishing service vs. raw, unburnished discs

AP Racing Championships in 2018:

JRitt@essex

Ferodo Racing's DS1.11 (compound code W) has become the go-to pad for the 991 GT3. We have hundreds of satisfied 991 GT3 and GT3 RS owners all over the world. The DS1.11 is moderate mu, easy to bed-in, and it lasts a fairly long time. We have never heard of anyone fading them on a Porsche, or any other platform for that matter. In summary, it is extremely user-friendly, and is an excellent choice for the 991 chassis at various power levels, with numerous tire choices, etc. One of the DS1.11's greatest attributes is that is much easier on discs than many competing products, and it doesn't have nearly as many issues with vibration and judder like many other brands.

We are also getting ready to introduce the Ferodo DS3.12 (compound code G). It is a higher mu compound with the flattest torque curve we have ever seen. It will have more bite everywhere vs. the DS1.11, and it will last longer. We will be adding info on the DS3.12 to our site very soon.

The Ferodo DS2500 (compound code H) is about as close one can come to a true hybrid street/track pad. It can be used for light track duty, but also has great street manners. It is almost silent, with only the occasional squeak during the final roll-up to a stop. It has good cold bite, which makes it an excellent autoX and daily/weekend driver pad.

The Ferodo pad part numbers for the 991.2 GTS are as follows. These shapes will work with the OEM discs our our Essex Designed AP Racing J Hook Discs. These pads are in stock and ready to ship today:
Front= FCP4664
Rear= FCP4713

We will be adding all of the other 991.1 and .2 applications to our site in the coming days. If you need pads in a hurry though, please give us a call (704) eight two four- 6030 and we can get you sorted quickly.

In the meantime, you can see more about the Ferodo pads our website, and in the video below: https://www.essexparts.com/brake-pads/ferodo-brake-pads

Tay101

Awesome! I have been waiting for these.

4 Point 0

You do realise GTS comes stock with 350 in the front? Was hoping for a 380 front and rear.

JRitt@essex

Yes, we absolutely do realize that the OEM front discs on the GTS are 350mm. Our brake systems are built from a racing mentality. In the pro racing world, teams scrap and scrimp to remove ounces of weight from their cars. Anything that is larger than necessary to get the job done is simply dead weight to drag around. That is how we approach our designs. If you want to go faster and a 14" disc will work, a 15" disc will simply add weight, increase the moment of inertia, and hinder wheel fitment. Sure it will look pretty behind 20" wheels, but that's not what our product line is about. Our discs are about efficiency, weight savings, cooling capability, increased longevity, and reducing long-term running costs.Heavy duty AP Racing J Hook discs in the 350x34mm size range have been used to win championships on cars far more demanding on their brakes than a 991.2 production car. For example, the Action Express Corvette Daytona Prototypes won the championship several times on our 355x32mm AP Racing discs, which have similar thermal mass to the 350x34mm. Yes those cars are significantly lighter, but they're also significantly more powerful and far faster (one hit 223 mph in testing!). The DP’s will absolutely give the discs a harder workout in a 24-hour race vs. a 20 minute DE session!

Keep in mind that the amount of energy transfer (changing kinetic spinning energy from the disc into heat) in a braking event is impacted more by speed than it is by weight. I'm going to get a bit technical here, so feel free to skip ahead if you feel your eyes glazing over! The core formula for kinetic energy is: kinetic energy = vehicle weight x vehicle speed^2

Take note of that little superscript at the end. If you look at the equation above, you'll note that doubling the vehicle's weight would double the kinetic energy but doubling the vehicle speed would increase the kinetic energy by a factor of four! In plain English, that means a stop from 220mph on a lighter car is going to be far tougher on the brakes than a stop from 140mph on a substantially heavier car.

To give you another example, our small four piston C6 Corvette Kit has found its way onto quite a few C6 Z06's pushing 600hp at the track. That kit features a 325x32mm disc. The OEM front disc on a C6 Z06 is 355x32mm. With a disc that is 30mm smaller in diameter than stock, many of our customers are seeing huge increases in pad and fluid fade resistance, less disc cracking, longer disc life, pads that wear longer, etc. Again, it's not just disc size that matters. It's all about design, optimization, and the resulting efficiency.

When comparing discs, you can't simply look at the outer diameter and decide that one will be more effective than another. The number of vanes, air gap, wall thickness, vane shape, metallurgy, hat attachment design, etc. all must be considered. In summary, our 350x34mm disc is going to be incredibly more capable than the OEM disc of the same overall dimensions.

Brake Bias

Also note that for our replacement 2-piece discs, we wanted to stay as close to the OEM disc sizes as possible if the vehicle is going to retain the OEM calipers. Why? If you retain your OEM brake calipers and change disc diameters, you are altering the front-to-rear brake bias (unless you had precisely the same increases on both the front and rear of the car). For many years it has been extremely common in the Porsche world to grab OEM bits from the GT3 cars and slap them on the other trim levels with complete disregard for what that will do to brake bias. Brake bias is a complex discussion, but here is the uber-abbreviated/simplified version.

The three factors that impact brake bias are piston size, disc effective diameter, and pad mu. Let’s look at the front of the car. If you put a larger diameter disc on the front and leave the OEM caliper in place, you will increase the front brake torque output, effectively shifting brake bias to the front of the car. Why? Because you are increasing the lever arm of the front disc by having the calipers clamp the disc further out from the hub. In other words, the front brakes will now be doing more than their intended share of the work compared to the rear brakes. If you went to a larger front disc and wanted to maintain the intended factory front-to-rear brake bias, you would need to decrease the size of the front caliper pistons to counteract the increase in disc diameter (that’s precisely what a properly designed big brake kit does, and what we do in our complete brake kits with AP Racing calipers). In the Porsche world the problem is often exacerbated by adding calipers with larger pistons. A six piston caliper with more total piston area replaces a four piston, and it is added to a disc with a larger effective radius…a double whammy of increased brake torque output on the front axle of the car!

So why is getting away from OEM brake bias bad? Because Porsche engineers spend quite a bit of time dialing in the car at the factory brake balance, and several systems are tied to that brake balance with ABS being the primary one. Substantial shifts in brake bias can create cause odd ABS intervention, funky stability control issues, accelerated front pad and disc wear, a long pedal due to increased fluid displacement to the larger pistons, etc.

But doesn’t your 2-piece disc kit increase the rear disc diameter vs. stock?

Yes, but only slightly. There is typically a narrow window of acceptable change in brake bias before things start to go wobbly. The size of that window varies by manufacturer and is tied to the ABS programming. In this instance the slight increase in rear disc diameter (330mm to 350mm) creates a small shift in brake bias towards the rear without any dramatic impact on ABS, pedal feel, etc. It is a far smaller (and more appropriate) shift than what we’ve seen people do in the past when they’ve drastically increased both front disc size (380mm for example) and compounded that bias shift by adding front calipers with considerably greater piston area.

Yah yah, that’s nice, but I still want bigger discs behind my dubs!

For some people the physics matter, and for others, they just want something that fills up their wheels. There’s absolutely nothing wrong with that! If you want to go bigger, we have you covered with our Essex Designed AP Racing Radi-CAL Competition brake kits. We created a separate thread about them elsewhere on this forum: https://rennlist.com/forums/991/1111...for-991-a.html

In our complete AP Racing brake system we use 372x34mm front discs, and 365x30mm rear discs, both substantial increases in diameter over the OEM fronts (330-350mm) and rears (330mm). When we launched these systems a few years ago, we specifically designed them with these disc sizes because they are about as large as can comfortably fit inside an 18” wheel. I won't go into all the merits of doing so, but obviously unsprung weight, lower rotational mass, cheaper tires, etc. all factor in. As noted above, despite being larger in diameter, the discs in our brake systems weigh less than their smaller diameter OEM counterparts. For example, the front 350x34mm OEM 991.2 GTS disc weighs 25.2 lbs., while the front 372x34mm AP J Hook disc in our brake kit weighs roughly four pounds less at 21.2 lbs. How is that possible? The height of the swept area on the OEM discs is 66mm, while that number on our brake system is 54mm. Making the disc face shorter removes a considerable amount of mass from the disc.Although our systems increase the brake disc diameters, we take that into account by adjusting the piston sizes in the AP Racing calipers, which maintains proper front-to-rear brake bias. Our systems offer both larger disc diameters and optimized brake balance.

So now I’m really confused…which is right for me, your 2-piece discs or your complete brake kit?

That depends on several factors. One must first determine their needs based on how they plan to use their car. If you’re going to keep your car fairly stock, run street tires, drive 6/10ths for twenty-minute sessions, and run tracks that aren’t terribly tough on brakes (Willow Springs), you may find that our 2-piece discs mated to your OEM calipers with some Ferodo pads and good quality fluid will be more than ample. If however you plan to mod your car to make it considerably faster (more power, suspension, weight reduction, slick tires), and you’ll be driving flat out at Watkins Glen for forty minute sessions, you may find that you need more. Or, you may not. There are a lot of factors at play. We created a video on this topic that you can see in this link titled, “Know Brakes 7: How to Plan for Future Brake Needs.” https://www.youtube.com/channel/UC-n...IT3tzOQ/videos

Our complete brake kits bring a whole bunch of other benefits to the party that can’t be found when using the OEM calipers. The AP Racing calipers are incredibly lightweight (front is 6.1 lbs. vs. 9.3 lbs. OEM unit), they have ventilated stainless steel pistons (dramatically reduces heat in brake fluid), anti-knockback springs, high temperatures piston seals that require less frequent replacement, more pad compound choices, and they don’t need to be removed to change pads. Those features add up to greater heat resistance, greater durability, less unsprung weight, less potential for fade, and less frequent servicing.

For many of our customers, other factors come into play as well. Most of our Porsche customers are successful professionals who at this stage in their lives value time as much or more than money. When they go to the track, they want to spend as little time as possible wrenching on their car, and as much time as possible driving their car. They want their brake system overbuilt and maintenance-free. Our complete brake kits ratchet up the overall thermal capacity and cooling capacity of the system. Because they run cooler, they use up pads, discs, and fluid at a slower rate, extending the time between servicing. When the pads do need to be changed, it takes longer to raise the car and remove the wheel than it does to actually change the pads. The calipers also don’t have problems with cracking ceramic piston caps, frequent rebuilding due to leaking piston seals, etc. that we’ve seen on the 991 GT3.

In the end, most of our customer find that our complete brake kits pay for themselves in consumable costs alone over the course of a few seasons. During that time, they also require far less attention and service, and they are more consistent, repeatable, and confidence inspiring than the OEM brakes.In summary, which path you choose depends on a wide range of factors in your situation. Of course, we are happy to discuss your goals with you and help you choose the correct brake products to match your needs and wants. That’s exactly what we do!

4 Point 0

Wow, Thanks for the epic response. I did know most of that. GTS already has 6 pot upfront. You guys have just taken so long to get something out.

I wanted to do something before i cooked the stock pads. I bought pagid yellow RSL29 pads about 4 months ago, and never fitted them, waiting for someone to have a real solution for the GTS.

I was forced to fit them as the brake light came on. Fitted the fronts and the light was still on. Oh Crap, the backs went at the same time. Rear engine I guess. First car ever that the front and rear OEM stock pads went at the same time front and rear. So I ordered the rear yellows two weeks ago.

If I went with the upgraded J-hooks, do they take a different shape pad to OEM shape pad. (By the way it took pagid three times to get the right shape pad to me on the front. They had the wrong shape listed for GTS)

With yellows all around, and my car heavily modified, and the way I drive, these stock rotors are on limited time. I doubt they will last another 6 months.

P.S. I boiled the stock fluid, on the very first spirited run I went on. Been running Castrol SRF ever since. But at the track I experience pad fade. They get too hot and the gas bubble between the pad and rotor, and the car doesn't want to pull up. Having the yellows up front made an instant huge difference.

JRitt@essex

No worries at all. Yes, we are just buried with projects right now, and haven't gotten to this application as quickly as we would have liked. It's a good problem to have in some ways, but not in others for sure!

We are test fitting our discs on a GTS this Wednesday, 2/27/19. They are an existing fitment, so if they fit properly they will be available for purchase immediately.

Factory fluid and pads are a no-go for track use. We tell everyone not to even bother trying.

Our discs can run as much as a couple hundred degrees cooler than an OEM disc. That difference dramatically drops the temp at the pad/disc interface, and can definitely mean the difference between fade and no fade. The 2-piece discs may be enough for you, or you may need the bigger discs of the big brake kit. If you PM more details on your car, tires, tracks you're running, etc., I may be able to give you a little better guidance.

Thanks!

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fsmich

Could you post or PM me the correct RE10 part numbers for the S/GTS 991.2. I also have them on order and would like to avoid "the car on stands" gig.