Tom@TPC Racing

I have heard of a number of people on internet forums using generic brand plain rotors intended for Cayenne fitment, which happens to fit .1 front. Personally I feel timid about braking at 150mph with $100 rotors... that's just me.

audipwr1

I use stoptech slotted blanks for $100 each on the front. Brakes way better than OEM

CosmosMpower

I like the price for that. Do they have rears as well? Which vendor do you buy the Stoptech blanks from?

CosmosMpower

I ran $25 a piece blank centric rotors on my E36 M3 before, no issues. Price alone doesn't dictate quality. There are some junk rotors out there that are cheap and $$$.

Tom@TPC Racing

Gents, I didn't say people weren't successful with it. I'm just a parts snob. ...again, that's just me.

JRitt@essex

Hello Gents,
We (Essex Parts Services) are just preparing to release AP Racing Heavy Duty J Hook discs for the 997 GT3 platform. As Tom from TPC mentioned, AP Racing discs are widely considered the most durable option in professional racing. Over the years they've won countless races and championships in ALMS, NASCAR, DTM, Rolex, etc. AP Racing has also won over 750 Formula 1 races with their brake and clutch products.

We are the exclusive importer and distributor for AP Racing competition brakes in North America. We are using the same designs, materials, and attachment mechanism for these discs that we use in pro racing.

The first sets should be will start shipping next week. We'll have discs to cover all 997 GT3's:
350x34mm Front: Retail $1398 per pair, iron replacement rings $349 each
380x34mm Front: Retail $1798 per pair, iron replacement rings $399 each
350x28mm Rear: Retail $1398 per pair, iron replacement rings $339 each

I wrote this post in the 991 GT3 section which contains many of the details about the product and our company. Everything in that post essentially applies to our discs for the 997 GT3. Our goal was to produce the most durable and most available disc on the market, and I believe we've done just that.

We're working on the web pages for these specific discs, and they will be done soon. In the meantime you can get a feel for the product by viewing our other exotic applications here.

Please shoot me a PM, email me, or call me at seven-zero-four-824-6030 if you're interested in a set of these discs.

Here are a couple pics of the 991 GT3 front discs...997 GT3 discs look similar.

CosmosMpower

J hooks are good but not cheap. A lot of the GT-R guys use them to stop their 600+ hp 4,000 pound track cars.

audipwr1

Someone educate me on how different iron disks of the same approximate mass can generate different cooling capabilities? Is the fin'ing creating better braking?

If I took out car and did 10 stops starting at 100mph at just under lockup with my $100 specials and the $1.5k big boys rotors what am I going to see on data logger?

DKP 97 C2 Coupe

I have been running the Brembo Type III's both front and rear with Pagid PS 29's for a couple of years now and couldn't be any more pleased with brake wear, feel or effectiveness. I think that this setup is bomb-proof for our cars but also offers excellent wear and durability characteristics.

JRitt@essex

Two discs of a similar overall mass or dimension can offer vastly different performance under all usage conditions. The function of the brake disc is to rub against the pad and create friction. The kinetic energy of the spinning disc is turned into heat. The disc’s function in the brake system is to absorb and evacuate that heat. Think of heat as flowing through the brake discs in a few ways:

•Conduction- The transfer of heat through one component physically touching another component. Disc heat flowing from the disc face (the part contacting the brake pads) into the internal disc vanes is a good example. Another would be the heat flowing from the disc face into the disc hat, then into your wheel hub and bearings.
•Convection- Transferring heat through fluid flow. In brakes, airflow can be considered the fluid. The air moving through the disc vanes absorbs heat and evacuates it on the outer edge of the disc.
•Radiation- Heat emits via waves into the air. Put your hand six inches from brake disc that just came off the track, and you'll feel massive waves of heat on your hand. As the temperature goes up, radiation increases and becomes the main way that heat is shed from the brakes.

Again, it starts with the friction that is generated at the interface between the pad and the disc. A larger disc mass provides a larger heat sink that can store more heat. This is accomplished by thicker disc walls and/or a larger disc diameter. More effective/efficient vane designs allow for greater cooling airflow, and allow more heat evacuation from the disc via convection. Superior vane design also speeds the flow of heat through the internals of the disc (convection). Greater disc surface area allows for more direct contact between the disc and the cooling air surrounding it (radiation). An aluminum disc hat slows the flow of heat from the disc face to the wheel hub, whereas an iron hat transfers the heat into other components more readily.

When we design a brake disc we look at the following:

Metallurgy- The specific iron alloy from which a disc is constructed. Over the past 50 years AP Racing has developed an alloy ‘recipe’ that is extremely crack-resistant and resilient when heated to track temperatures. Different materials are added to the mix to increase durability.

Internal vane style/shape- The shape of the internal vane has a huge effect on how much air a disc flows, which largely determines how hot or cool it runs. Most pedestrian discs have a pillar vane that looks like the one below. While this type of internal vane design is cheap to manufacture and creates a stable disc face, it doesn’t flow much air. The next step up the food chain in terms of airflow would be a straight vane disc. It will flow more air than a pillar vane, but the vanes are not directional. A directional vane disc is handed for each side of the car. The shape of the vanes is optimized to flow the maximum amount of air when spinning in a certain direction (think of them like the blades of a fan).

Number of vanes- Cheap discs typically have a low vane count…24-48 vanes in most cases. Pro-level racing discs typically have 60-84 vanes depending on the application. A higher number of properly designed vanes increases both airflow and disc face stability. That means cooler running, less deformation under high heat, and more even distribution of pad material on the disc face= less chance of judder or vibration.

Disc wall thickness and air gap- These factors are manipulated to adjust the durability, overall mass, and airflow in a disc. A heavy duty racing disc tends to have thicker walls for greater heat absorbtion and crack resistance, and/or a wider air gap for more airflow.
Hat material- An aluminum disc hat slows the flow of heat through the disc, and typically lowers the overall unsprung weight. Less disc mass is easier to both accelerate and decelerate.

Hat attachment mechanism- There are many ways to attach a hat to a disc. The cheapest discs are one-piece design. The hat and friction ring are all one hunk of iron. They’re heavy, don’t flow much air, and tend to have a narrow air gap. A dual-cast disc (like the OEM GT3) is a step better. A fully floating disc is superior because it can more freely expand and grow when it is heated at track temps.

Slot/drill pattern- Slots or drill holes are designed to give a pad more places to bite into a disc. Drill holes tend to crack, and slots are better for heavy use. It doesn’t matter if the holes are cast into the disc or machined afterwards. Drill holes create stress risers that crack. Straight slots leave gaps between them around the disc, creating temperature gradients (hot and cool spots). The AP Racing J Hook design was created to evenly distribute heat throughout the entire disc face, lowering the overall stress on the disc as it heats and cools= less cracking.

I won’t even touch this one…but the actual manufacturing of a disc has a big impact on how it performs as well.

I’d recommend checking out our actual disc product page for in-depth explanations of the features and benefits I mention above:

Also, I wrote an article a while back that compares the OEM C7 Stingray discs vs. our AP Racing Heavy Duty J Hook discs. It gives some good insights into the differences between plain-jane, cheap discs vs. high performance ones.

So what does all of that mean, and what will you see on your data logger after 10 stops from 100mph?

In a 10-stop strategy you actually may not see any difference, unless you have the ability to collect real-time disc temperatures with a thermocouple. Extend it to 20 stops however, and you may see a glaring difference in stopping distance due to brake fade.

The components in the brake system are a chain. The disc has to deal with heat, but so do the pad and the caliper. The pads absorb heat and radiate a massive amount of heat into the air around them. The pad backing plates are touching the pistons, so heat flows into the pistons. The pistons have brake fluid behind them, so the heat flows from the pistons directly into the fluid (why stainless steel pistons are a huge help, since they dramatically slow the heat flow). That's also why titanium pistons are used in high-end race calipers.

If you keep your disc temps down, you reduce the amount of heat flowing into the other brake components. That reduces the possibility of pad or fluid fade, increases brake repeatability/consistency over a series of stops, which ultimately increases driver confidence. Good racing discs will also run at lower temps for longer, resist cracking for a longer service life, and add a large amount of convenience because they won’t need to be replaced as often. Also keep in mind that cooler discs means cooler pads that don't wear out as quickly or need to be swapped, as well as less boiling and bleeding of the brake fluid.

I've had customers on other platforms crack $100 discs every weekend (the C5 Z06 comes to mind), install our discs and have them last an entire season or longer. If you look at the initial cost of two-piece discs, it always appears high. If you do the math over a couple years however (how long most track-junkies own their car), you typically find that the long-term running costs on the higher end brake components is actually lower. You spend less, fiddle with the brakes far less, see benefits across all brake components, less wear and tear on hubs and bearings, and you get to enjoy the benefits of the discs themselves during the period of ownership.

Last but not least, two-piece discs have residual value because the hats are reused. If you sell them to someone else, they can get new iron rings and they're good as new. If you get $0.40 on the dollar when you sell them, your overall investment is still greatly diminished. When your $100 discs are cracked, they're trash and you never recoup any of the money spent on them.

paver

JRitt, awesome post...thanks for the info. How many times can hats be re-used in a DE environment?
Is it possible for some pads to crack rotors worse than other pads?

audipwr1

Very thoughtful post - appreciate it.

As an aside we had Stingrays at Bondurant and I nuked two front calipers in 2 days of driving on them. The brakes on that car are horrible and overheat unless you baby them, like 3 laps and already can feel fluid overheating

I think with that car its probably cooling that is the main problem, I would do two easy laps to try to cool the brakes before going hard again and that didn't make a big difference, do that on a GT3 and they are fresh again

Also I like the idea of doing some data logging on braking performance over a simple layout of accelerate and braking.

My $100 specials certainly have fewer vanes and are solid centered (which of course means initially up to some point they will run COOLER than yours because they have more mass to absorb the heat)

JRitt@essex

It's hard to put a firm number on it because conditions vary so great. I guess the best way to explain would be to give a couple examples:

In summary, wear of the disc hat shouldn't be a concern at all.

As for some pads causing more cracks...that really isn't an issue either. Heat cycles are what crack discs. When a disc is taken to track temps it expands. When it cools, it contracts. The constant expanding and contracting of the iron is what cracks discs. In the ideal scenario, you would run your discs at a constant temperature...let's say 900 degrees F. That's why you see pro race teams controlling their brake ducts. Sometimes they run them wide open to allow the maximum air into the disc. Other times they tape them halfway shut to limit air...other times they cover them completely. It just depends on the track and the temps they're seeing. Wild temperature swings crack discs.

The impact of pad material would be more along the lines of grooving, marring, or depositing unevenly on discs. If you drive abrasive race pads cold, they tend to chew up discs fairly quickly, since they weren't designed to be run in that temp range. In that case, they're working almost purely in their abrasive mode. When you heat them up, they start to stick to the disc, creating a pad transfer layer on the disc face...that's the adherent mode. If you run a particular compound too hot past it's max operating temp, then it may melt and come off in globs on the disc face. Those splotches cause uneven/high spots. Every time that spot 'goes past' the caliper when you're squeezing the brakes, you feel it as a vibration or judder. All of that said, some compounds do run a little hotter than others due to their material composition (sintered would typically run hotter than an organic pad for example), but most of the interface with the discs would be as described above.

JRitt@essex

No worries and thanks for the input on the Stingray. Two-three laps is about what I would expect based on the numbers. If you read my analysis, I was rather unimpressed with the brakes on paper. My expectation is that they'll be problematic for owners in the coming years. I'm fighting the usual reluctance on the corvette forum, as some people are reporting no problems. My hunch however, is that they're not using the car anywhere near its limits. I've seen many posts in which the driver said he's driving at 9/10ths, then I watch the video and they're coasting into turns and running 8 seconds per lap slower than a pro driver did for the same car in a magazine test.

The GT3's 380x34mm disc is definitely a far bigger heat sink than what is on the front of the Stingray. Even the standard 350x34 is considerably larger (the base Stingray is 320x30mm). Due to the rear engine layout the GT3 will be relatively easier on the front brakes than the Corvette, but the front base Stingray disc really is too small for serious track use given the car's capability. The Z51 discs are only a little better.

Data is the one certain way to see what's going on. Logging disc and caliper temps can give good insight into what's actually happening at the corner. FYI...real-time temps are best. By the time a car does a cool-down lap and enters the pits, the disc temps drop hundreds of degrees. On a good disc that flows a lot of air, temps plummet very quickly.

MC 968CS

Hi. Regarding the rear with a floating hat, does the handbrake still work if fitted to a street car?

350x28mm Rear: Retail $1398 per pair, iron replacement rings $339 each


This is why I ask. It's got a custom engineered hat i think. http://www.prtechnology.com.au/produ...andbrake-drum/