It is normal for race brakes to squeal. Its not a 'problem'.

 

Guys, let's add a little logic to the equation and not get sucked in to poor thinking and nice cosmetics (my rotors are bigger than your rotors, I have more pistons than you ...). One big caveat (although I doubt I need it), I have not been to the track with an ABS car so I could be wrong.

If your stock piston/caliper brakes WITH ABS can get the wheel to lock up, you cannot improve stopping distance or stopping power!!! Please read the last sentence again! Clamping force or anything else is irrelevant! Brake feel or modulation is really unliekly to be a big factor. If your car has ABS, you have to apply pressure to transfer the weight and then stay jammed on the pedal. Only during the weight transfer transtions phase (very quick) could mudulation have a factor. After that, stand on 'em.

Obviously this argument goes out the window on non-ABS cars like my Countach where modulation is critical. On any car, you are strictly tire traction limited and al long as your brakes can lock the wheel up, that's all the stopping power you've got.

The only thing that matter is temperature management (or brake pad wear but I will skip that argument for now). If you are having temperature problems (brake fade, ...) the first thing you should go after is increased cooling. Only after increased cooling fails should you go to larger rotors, bigger calipers, etc.

Now, temperature problems can be broken down into two categories, transient and buildup. Transient is the system overheating because it can't absorb the heat spike from a huge brake, 160 - 40 mph. If this is the case, larger calipers, rotors, and pad area will increase the transient handling capacity. Cooling has less of an effect here because the heat buildup is so quick. This could be a problem with stock brakes, I don't know, but I will next summer. Pad selection comes into play here in the temperature range and how the coefficient of friction changes as a function of temperature. Others should be able to comment about stock brake track performance.

The second problem is heat build-up over time because there is not enough cooling between braking zones. This is often track dependant and is easily fixed (normally) with increased cooling, i.e. ventilation. Obviously pad selection can also affect this. The easy answer here appears to be the GT-3 ducts.

A real interesting side bar is that more piston area (4-8 pistons) could actually hurt the ABS system as it is assuming a certain volume displacement to achieve a certain pad/pressure movement and that could change the desired optimum operating window. I will try to find my brake expert.

Please don’t think bigger brakes will be better unless you have had a specific problem that cooling want fix. Now, if you want them for bling, OK, but say so and don’t offer bogus driving reasons.

 

Absolutely. My racecar's brakes squeal like Ned Beatty in Deliverance. But, I'd really like to avoid that on the street car!

 

Tim -

I've made the same argument as you regarding lock up for years. I've also noticed that in tuner shoot outs, the big brake kits rarely make any difference at all in terms of (one time) stopping distance.

That said, here's an interesting counter argument from the Baer brakes website.

Disclaimer: I'd say what Baer says to if I were selling brakes. But, still, there may be some merit to what they say.

"Although virtually any brake system can be spiked into locking a rotor or activating the ABS, the true measure of a performance brake system is how close it allows you to come to the point just shy of locking. This is affected by a number of elements. Some of the most important are caliper stability and leverage affect on the rotor, which increases with rotor diameter. In simple terms, the more stable a caliper and the more evenly it can apply the pads to the rotor surface, the faster your car will stop."

 

Brembo's firm pedal comes from a few different areas. The most obvious are the piston diameters and the stiffness of the caliper. The larger the piston the more fluid you need to move them. Also if the caliper has flex that movment can be felt through the pedal.
There has to be balance though. Too small of piston diameters will give a firm pedal but you will lose brake torque.

A good portion of Brembo's firm pedal and awesome modulation comes from their floating pad design. This is hard to explain in words but basically the pads sit freely within the caliper body on two pins. Atop the pads lay a spring clip that holds the backing plate of the pad against the pistons. When the pedal is applied the pistons press the pad against the rotor. When the pedal is released the pads move completely off of the rotor. The pressure from the spring clip ads to the firmness. The advantage is smooth modulation. The is no play in any of the moving parts to distort the feeling. Also because the pad moves completely off the rotor there is no "off brake drag".
This is a function that will only be found in a Brembo Gran Turismo Kit.

ColorChange-

Pedal feel and modulation are the main reason for why I upgraded to my Brembo's. Yes I can out brake my tires with my stock brakes. The difference is the amount of control and modulation I have with my Brembo's. I can control the amount of braking force all the way from initial application to lockup without skipping a beat. On the street I have a faster response and quicker reaction times. This combined with the fact that I cannot fade my brakes in the canyons or on track make it a must do upgrade. Oh, and the weight savings. I saves 36 actual lbs. by upgrade my brakes. Unsprung, that equals 98lbs. Rotational weight savings is even higher.

$6000 was a drop in the bucket for the amount of performance, looks and safety I got from 1 upgrade.

 

Thanks for the response Latebraker. So, do you agree with Colin that the 4 piston caliper would have better feel than the 8 pistion caliper? I'm still fuzzy on why that would be...

 

Tim -

For me, part of the benefit of upgrades (on a street car) is just the feel. For example, I don't use all 680 ft lbs of torque very often. And I will probably never do a full qtr mile run (nor an open track event) in the 996TT. But, even in just the brief seconds of acceleration that I do, the feel of 680 ft lbs is much more exilerating than the feel of 400+ ft lbs. Similarly, the feel of the coil over suspension is much improved vs. the stock setup. The car turns in better and exhibits less understeer - although I don't push the car to its limits as I would on a race track (in a cheaper car that already has road rash, etc., but I digress ).

My feeling is that the same will be true with the brake upgrade - although I could be wrong to the tune of $6K (and that would suck! ).

P.S. After racing for 8 years, I would never, ever take a car to the track unless I could walk away from it - totaled - without feeling the slightest bit of mental anguish. I would feel way to much mental anguish if the turbo bit the dust. Another problem with racing experience is that it is no longer fun for me to just hustle a car around a track. If I'm not racing wheel-to-wheel, I'll probably fall asleep and go off track.

 

Without a doubt. The 4-piston is firmer than the 8-piston. I asked one of Brembo's engineer's this question and almost wished I didn't.

It has something to do with the displacement of pressure from the pistons. The 4 piston caliper has larger pistons but requires less pressure to create the desired brake torque. The 8 piston caliper has more pistons therefore they can be smaller. Smaller pistons take less fluid to move but require more pressure achieve the exact amount of clamping force (brake torque). Somehow this translates to the pedal and dictates the exact feel.

Did that make sense??? I don't know.

If that didn't explain it then you can take my word for it. I drove both. The 8-piston was incredible at higher speeds. It scrubbed off mph's incredibly fast from the triple digits. Slower more technical stopping was not as precise and required more pedal travel. The 4-piston was incredibly firm. Still subtracting speed incredibly quickly. Slower, technical brake zones were not an issue. Precise braking with perfect control. Great feedback and readability from the tires and brakes.

 

Funny but true. Great insight Racer and latebraker on the pros and cons of different brake setups!!!!

 

I think so. Thanks for your sharing your insight.

One last question for you. Is $2500 really a realistic price for my stock brakes? (and who would likely buy them?) If so, it makes it a much easier decision!

Thanks again!

 

Contrary to what latebraker has mentioned, I have had the 6 piston calipers for some time now and it has performed great so far. From my experience with the Brembo set ups on other vehicles, I have had a slow and soft pedals with Brembos. Unable to ever have this problem resolved.

After speaking to other 996tt owners with the Brembo GT conversions have also mentioned that they now have experienced a slower/softer pedal.

The 6 pistons have never faded on me yet, always have had a rock solid pedal and very quick pedal.

After experiencing fade with the stock 4 piston and looking for a brake upgrade I opted to go with the GT2/GT3 6 piston set up. Weight of GT2 6 piston calipers
(8.06/3.66 Lbs/Kg for GT2) vs. (7.98/3.62 Lbs/Kg 993tt 2 piece big reds) The weight difference was minimal, although the 350mm rotors were a few pounds more than the stock 330mm.

As a side note, the green pads for track days have worked well. The yellow P90 pads work OK for the track, but do not last.

With so many combinations of 6 piston set ups you have to get the correct calipers and carriers to work correctly.

Also the rear calipers are different in design than the stock, different part numbers.

 

Oak -

Where did you get your brake upgrade? What are the part nos? Might as well do the comparison shopping while I am at it.

 

Racer 63 , I have PM'd you.

 

I thought I would throw in my $0.02 here. I will try to explain the mechanics at work here.....

Brake Torque
Brake torque is simply the friction force of the brakes multiplied by their radial distance from the center of the hub. So, with all else being equal, the large the rotor, the greater the brake torque. That said, let's start changing the other variables.............

Brake Pad Friction Force
The brake pad friction force=the resistance of the pad/rotor interface to sliding. Basically as the pads squeeze the rotor, friction develops in direct proportion to pistons' pushing force on the back of the pads. The pad friction force (the force that brakes the rotor) is defined as the piston force multiplied by the pads' coefficient of friction. I will explain the piston force shortly. The coefficient of friction is a function of the pad material, rotor material and the temperature of both. This is why they sell different pads.

Piston Force=Clamping Force
The piston clamping force is defined as the sum of the piston bore areas along one side of the caliper multiplied by the brake system pressure. The bore areas are a function of the specific calipers used.
The GT2/GT3 6 piston setup uses 28mm, 32mm and 38mm pistons respectively. This equates to a total (one side) area of 2,554 square millimeters.
The Brembo Evolution GT (8 piston) setup uses 32mm, 32mm, 38mm and 38mm pistons respectively. This equates to a total (one side) area of 3,877 square millimeters.
This means that the Brembo Evolution GT (8 piston setup) has approximately 52% more piston area than the 6 piston GT2/3 setup. For a given brake system pressure (the hydraulic brake fluid pressure that corresponds to pedal input), the Brembo 8 piston setup will generate precisely 52% greater clamping force than the 6 piston GT2/3 system. Stated another way, the Brembo 8 piston setup will deliver the same clamping force as the 6 piston GT2/3 system with less pedal force.

Pedal Feel
The beauty of hydraulics is that liquids are incompressible. Hydraulic (braking) systems work by translating the input force at the master cylinder and directly translating it to an output force at the caliper piston/brake pad backing. In general, brake modulation and pedal feel are a function of the hoses used to connect the rigid brake lines to the calipers, any pad "lift-off" devices or springs employed, piston diameter, and the temperature of the brake fluid (within working temperature or boiling). Rubber connecting hoses will bulge when pressurized by brake pedal input. This bulging is felt as a sponginess in the pedal. The distance the pedal must travel before initiation of braking is related to pad "lift-off" devices used that pull the pads off the rotors so they don't drag and also to the volume of fluid necessary to physically move the pistons. The larger the piston area, the more pedal travel necessary to move them.

Brake Fade
Brake fade is due to either boiling of the fluid or loss of coefficient of friction of the pad material with increased temperature. The brake fluid boils when the rotors and calipers cannot shed heat fast enough. In this case, the larger the brake components the better the heat dissipation. The problem is that with larger comes heavier. The heat actually boils the fluid which introduces vapor into the hydraulic system. As stated before, the beauty of a hydraulic system is its incompressible fluid. If the fluid boils and introduces vapor into the system, the vapor is compressible. There goes the show! So this is where improved brake cooling come into play.

 

Way to go Ken. I will send a lengthy response later today.