I have the 8-pot kit w/ 7k miles and not experienced any anomalous noise.

 

OK, now that everybody understands that bigger brakes will not stop your car faster (under normal conditions) we can discuss modulation. Hold on to your hats …

WITH 4-WHEEL ABS THERE IS NO BRAKE MODULATION!!!

That’s right. Here is how you drive with ABS. hit your brake point and JAM, STAND, PUSH YOUR FOOT THROUGH THE FLOOR. Stay there, when you hit your corner entry velocity on the right line, turn in, WHILE STILL STANDING ON THE BRAKES! The ABS system should brake far better than you ever can and you will drive faster, brake deeper than ever before.

Now, if you don’t think I’m a wacko from that statement you might say “what if I need to bleed off some speed�. Same thing, go full throttle, jam the brakes for a sort time (however long as needed to reach your desired speed, and move on. With ABS (a good 4-wheel ABS), it will do everything better than you ever could on your own.

Yes, I’m waiting for some old crusty racers to disagree with me. This only applies to ABS cars.

Racer63: The Baer statement only works if you don’t have ABS, then I agree completely. Also, their discussion holds more weight when comparing poor brakes you could get significant improvements with caliper strength but the stock calipers are awfully good. Also, I hope I don’t spend so much time at the track that only racing is fun.

Latebraker: Modulation is largely bogus. I will be able to prove it when I get my car and my data acquisition system installed. Like you indicated in your earlier post, the reason a smaller piston area (4) caliper feels firmer than a larger piston area (8) is that less volume needs to be displaced to achieve the same contact point and then clamping force.

As a general rule, you want to use the SMALLEST brakes possible to minimize unsprung weight. When do you need bigger brakes? When you can’t absorb the transient heat spikes as when coming down from huge speeds. First, go after big time cooling, then go to bigger hardware.

I am trying not to sound like too much of a jerk but I have been fighting so many misconceptions for so long it drives me a little crazy.

 

Tim -

Haven't had time to read the entire post yet. Will do so later. But, I have one important detail to add that will save people money. If you are running race tires, do NOT jam on the brakes. Despite all of the advantages of ABS brakes, modulation is still required with race tires, otherwise you end up with flat spots. The difference is that, with no ABS, you get one large flat spot. With ABS you get 4-5 smaller flat spots - which still royally screw the tire...

Your braking technique will most likely work with regular street compounds. But, I wouldn't try it with a race compound. (Actually, I did try it and royally screwed one of my best tires that day... Then confirmed the issue with other racers who said "duh, what did you expect!" So much for the magic of ABS allowing me to brake like M. Schumacher. )

Bottom line, for a street application, I buy your arguments. But, on the track, I have empirical data that what Baer says makes sense (at least with race tires).

P.S. Disclaimer. There is probably a really smart engineer out there who's figured out how to make an ABS system that does a better job of "electronic modulation" with race compound tires. But, this guy did not design the brakes on our stock TTs. And, the race compound-specific ABS system would probably be suboptimal for a street application.

 

I guess it's just a difference in opinion. I appreciate the control and modulation. I use it. I don’t want to rely on the ABS to do the braking for me. If my ABS comes on then I made a mistake.

To me this is like saying that traction control does a better job than I can do. Why not leave the traction control on, just stab the throttle and rail it. Porsche's PSM is a great thing but I don’t want to rely on it to dictate my driving style on track.

-ColorChange-
The general rule of wanting the smallest brakes possible is completely valid. Shaving unsprung weight is one of the best benefits of a brake upgrade. All of the Brembo kits do save weight over the stock brakes.

The 14" 4-piston kit saves the most weight (7.4lbs. per corner) but requires changing the wheel carriers. Retail on the 14" kit is $4995.

The 15" 4-piston kit is a direct bolt on. Retail is $3595. Less expensive. Only 1.2lbs lbs. heavier per corner than the 14" kit.

Brake torque from the 14 & 15 inch kits are very close. The 15" kit has slightly smaller pistons than the 14". The extra 12.7mm of effective radius gives Brembo the ability to use a smaller piston size to achieve the same brake torque while requiring less line pressure.

Brake torque is defined as (Piston Area) x (Effective Radius) x (Line Pressure) x (Brake Pad Coefficient of Friction).

On the 9996 TT upgrading to a larger disc was mandatory. First the 13.6" disc does not have the necessary heat sink ability. Second, upgrading piston area would have created a softer pedal and more travel. Third, there is no reasonable and cost effective way to increase line pressure. Lastly. A higher coefficient of friction would have created more heat and the 13.6" rotors would have been even less adequate. It was mandatory to enlarge the effective radius with a larger rotor and smaller pad annulus.

There is no disadvantage to any of the Brembo upgrades. If your driving style will benefit from it then it is worth doing.

 

Sorry Latebraker, fact - not opinion. If you are not using your ABS you are slower braking than anyone who does. The only caveat to that is if Porsche’s brakes are not true 4 wheel and the system sucks. I highly doubt this as they are generally regarded as the best stock brakes money can buy. But, I do not have the track data to prove it. I will. I am also getting the SAE Bosch handbook and I can supply more data - factual data - not anecdotal or opinion - if you wish.

Your data on the need to upgrade for heat reasons is possible, I just don't have the data yet.

If you want me to go into further explanation I will but just let me offer this. Your 4 wheel ABS will take each will to its maximum traction. This is not possible on any car without it. As you stop, you get longitudinal g shift and therefore changing brake bias so this forces a compromise in your brake balance. ABS optimizes that for each wheel, many times a second. You, driving with one brake pedal and fixed brake bias, are slower. Much slower, or else your ABS sucks, and I can't believe Porsche’s does.

Now, unsprung weight savings, I'm with you completely on that one. If your upgraded brakes are heavier, and you don't need the transient heat absorption, that is a drawback, otherwise, you're right on the no drawback claim.

Racer63, if your ABS was flatspotting your track tires, you had a bad ABS system. Any decent (last 5 year) ABS system never takes the wheel to lock up - which would flat spot the tire. The ABS systems typically kick in at about 20% slip, not 100% slip with could flat spot the tire. Also, current brake frequencies are around 100Hz so you will never see flatspotting with any tire. As a matter of fact, I have $1,000 that says you cannot flatspot a tire on your tt even if you try using your brakes (you might be able to do it with the PSM off and sliding the car sideway at 100mph).

 

Latebraker, I am assuming you upgraded your brakes after having thermal problems at the track. Did you go after cooling first?

 

Have you actually tried this yourself? I'm not the only one experiencing the problem in ABS cars. I have not tried it in a 911, but I wouldn't want to...

I'd take the bet if it didn't also cost me $1200 for the tires to run the test!

 

Racer63: No, you have me right now, I have not tried it yet but as I sadi before, I will and I will present the data when I dol. If you had an old ABS and not a 4-wheel system, you could very well have had those problems. If Porsche's system does this MAN will I be mad and light them up! I can't believe it will though.

 

I used the Weltmeister brake duct kit from Performance Products. It worked well but was not enough. The factory Turbo rotors have very thick walls. I believe Porsche does this to extend the life of the factory rotors. With the brake ducts installed it took longer to fade the brakes but once they started to fade they didn't come back. I believe that the rotors have the ability to absorb allot of heat because the thicker walls but they retain allot of heat as well making it more difficult to keep cool.

Now keep in mind that I was using Pagid Orange pads. They operate well up to 1000 degrees. It took a while to get them there, about 3 laps at ButtonWillow, but once they faded it took a full lap to cool them back down. I was also using Brembo's new LCF 600 brake fluid. I am very sure that it was not a problem with the fluid. The boiling point on the fluid is over 600 degrees. The pedal feel never changed. The feel was still firm yet the brakes would not grip.

I did go in steps before doing the Brembo upgrade. I went through 6 different pad compounds, 3 different fluids, two sets of factory rotors and the cooling ducts. I am very hard on brakes and I don’t hold back at all when I'm on the track.

 

Latebraker:

Sounds like you followed a smart plan and it looks like I will be upgrading my brakes to. I will probably wait to prove your data at the track first but I will definitely go after cooling now (GT-3 ducting sounds the best) and see if it will hold up.

Please tell me if you get a chance to drive your car like I am suggesting, hit your entry speed (should be higher than your non abs speed), and turn in with your brakes still stomped. I would love to hear how it goes.