Davidoff

I have now tracked my GT3 MkII at three trackdays and love it to bits, however on the second day about a month ago I managed to overheat the discs resulting in cracking on the cooling vent edges. We were running 20 min sessions on a short track (about 1.8k). I recall that I was pushing but I don't recall ABS cutting in as I was trying to work up to rather than beyond the limits. Therefore I was rather surprised to see the disc failure.

Any thoughts or similar experiences to share. Is this just a question of recognising that the brake system cannot cope with a 20 minute session of aggressive track work and therefore you need to mix hot laps with some slower one to cool the brakes? (Or am I just a crap driver....or both as I suspect).

Any advice / experience gratefully received as it should be of economic benefit (new set of discs imminent...ouch).

Dave

mds

I have been replacing cracked discs on my car, I just installed the third set. A set seems to last about 8 track days.

Guidance I am using on when to replace them comes from Porsche AG on 964 Cup Car Cast Iron Disks. Thanks to 993_996_enthusiast for the quote:

"Ventilated discs will develop small heat cracks with race use. These cracks will have no effect on braking. Discs must be replace (sic) when three or more adjacent radial holes are connected by cracks or the outside edge of the disc is cracked."

amondc

Get the Brake cooling ducts from Porsche Motorsports this will save your rotors. Its the same part on the cup cars

cosmos

I saw those ducts and did not notice a huge difference between the two. The Motorsport one just had slighty deeper grooves and was slighty deeper in height. I did not think thery were worth replacing the stock ones.

amondc

I havent compared the 2 but may be something to think about after the stock ones get ripped off. Which happend quite often

mds

I forgot to mention this: check to be sure that the internal disc vents are clear of debris. I've found chunks of rubber from the track can get sucked into the eye of the disc and clog up the vents. The blockages are hard to see, check carefully.

MJones

Best guess is that your braking technique in the root cause in such a short period of time.
Excess heat is built up from gradual to hard application (street style) instead of a HARD initial (threshold) application and trailing off (track style).

MatroxMGA

new pads will not generate as much heat to the rotors.......such as pagid or PF. The GT3 brakes must be better than most cars people use at the track, or??? Cooling is of course important for rotor life.

NJ-GT

I'm running PAgid Yellow Rs-19 and Castrol SRF. I'm also using the GT3 Cup car brake ducts.

So far, my breaks keep overheating but not as often as before.

I pointed out in a previous post that Porsche knows something that they think we don't. Take a close look to the pictures on the 05 Cup car. Did you notice the openings on the front spoiler lip? Yes, those ones that look like the ones in the 996Turbo and 996 C4S. Well, we don't have those holes, our cars are lower than the regular 996, and there is practically no airflow underneath our cars.

That's why Porsche installed the PCCB on the 05 Cup car. They know that by fixing the brakes cooling issue, the ceramic rotors will last longer. However, we steel rotors owners will get the benefits as well.

mds

A lot of people jump on the brakes very hard. I was always a guy who braked, for the most part, very easy. I didn't use up the brakes at all since I tended to roll off the throttle and onto the brake more easily. To put it in perspective, at Laguna Seca, which is hard on brakes, Rick Mears and I were teammates at Penske and Rick finished the race with only 70 thousandths of an inch of brake pad material left. I only used 70 thousandths of the pad in winning the race. People brake differently but can still run the same lap time, especially in a race.
- Danny Sullivan

FixedWing

I’ve heard this too but I am dubious.

Brakes convert energy into heat. They are pretty efficient at this. Slowing a car from 150 MPH to 50 MPH dissipates the same amount of energy and therefore produces the same amount of heat no matter how one goes about it.

If the amount of heat cannot be reduced, then the only way the peak heat might be reduced is if the brakes have more time to dissipate that heat. The only way that will happen is if one starts braking sooner and extends the braking zone.

But even that isn’t going to make a big difference. The steel rotors are big heat sinks. They absorb that heat instantly and then radiate slowly. After a while they will reach a peak temperature and be radiating their heat all of the time as the driver circulates around the track.

So I don’t buy the “brake technique” theory.

One other point is that heat issues have been a big problem with the GT3 for a long time. The Mk1 version was notorious for this. The Mk2 is improved but I don’t think that the problem is totally gone. It really relates to the body design and to the lack of serious quantities of cooling air in the wheel well. The heat ultimately has to go somewhere and without adequate airflow the rotors just grow hotter and hotter.

Stephen

cosmos

So why cant we (even with the radiators) cut holes from behind the front fender liners. I was looking at them at it even appears that a small recesion is there, just not cut out. I want to cut it out. Why should I not??

vegasgolf98

My mechanic is the head mechanic for the past two Le Mans winners. I raised this issue with him since a friend of mine only gets about 1,000 track miles on the steel rotors and then they are gone. He said that the drilled rotors won't last more than that period. The cars (all GT3's including RSR) have a brake cooling issues and drilled rotors only make it worse. These guys change rotors every race, sometimes two or three times.

He suggest only using the factory drilled rotors on the rears and installing solid rotors with "hats" for the track. The "hats" will make a rubbing sound on the street and will be annoying, but will last a long time. It is just either that or change the rotors. No real compromise sorry to say.

vegasgolf98

In other words, yes, breaking technique can make the rotors last a bit longer, but it most likely is not you it is the drilled rotors. My mechanic said don't waste your money on the cup coolers (almost the same) and still dont' help.

Davidoff

Thanks for the input. As I suspected, this is a very common problem.

From a logic point of view I would agree with FixedWing in that hard track style braking would perhaps create heat faster with less cooling time, but I cannot imagine that it would make much difference to the ultimate disc temperature.

In any event, I have fair amount of track experience and was using hard braking from threshold to release through turn in.

Another factor is probably a combination of dirt in the cooling ducts and the high air temperature here in Dubai (36 C + humidity). It is probably worth getting a metal probe to clean the ducts prior to tracking the car.