Anyone had more substantial track experience with the A4-sized drilled and vented A4 brakes? I have them, as does Steve S., but I've only taken them to Blackhawk which is a short track, was a short event, and didn't really test much of anything about the A4 mechanically.<p>Any input on these units? My fluid seems like the limiting factor still.<p>Cameron

BTW, the super blue is going in this week or next. I think after 4 driving schools...and 5 autocrosses...my car is overdo for a brake bleed. Might as well put the super blue stuff in that has been sittin in the garage for the past three months.<p>Steve S.<br>97 2.8QM<p>P.S. Jay has the same Brembo cross drilled rotor I have.

At 16 years old,your 'fluid' shouldn't be a limiting factor.

<br>do those with different rotors from stock believe that they've avoided the fate others on the board have suffered (replacement of warped original rotors) by using vented/drilled/larger/slotted rotors?<p>Needless to say, no matter how much cooling airflow is available to your brake assembly there will be thermal issues, the possibility of cracking or deformation. The near-inexcusable usage of the brake pedal many have (I'm not totally innocent here) on track days doesn't help.<p>Cameron<p>

nt<br>

That was Road & Track's platform in this last months mag. They said that the only way to really combat warping was to add mass to the rotor and that drilled rotors didn't add much benefit. The main issue seemed to be rapid heat cycling. This would make sense to me, as drilling or slotting doesn't really do much but give you spaces for gases and gunk to escape while reducing mass. My guess is that you need to go to bigger rotors to truly avoid thermal deformation due to overrapid heat cycling..

i had a 91 laser turbo, and i have tried the following:<br>( the 91 stock had 10.4IN rotors, single piston calipers) over 7 years, averaging 1 set of rotors on the front every 9 months.<p>1/ Slotting. Supposedly removes gasses, and cleans your pads. Went through pads super quick, but rotors still warped.<p>2/ Drilled. I went through different patterns, from symetric to asymetric, agressive, mild. The more holes i had, the easier it seemed to be able to crack the rotors. and radiused holes are a must, seems to relieve stress and reduce cracking tendencies. Rotors still warped<p>3/ drilled and slotted. Again different patterns, still warping.<p>4/ Dual piston calipers, bigger pads (larger swept area), 11.5 in rotors, cross drilled (stillen). Bye bye warping. <br>The dual piston calipers and larger pads meant more friction area, as well as heat dissipation. Same with larger diameter rotors.<p>Couple of driving habit things:<br>1/ coming off highway, don't leave foot on the brakes at the lights. This creates a hot spot where the pads are gripping the rotors. (uneven heat = warping)<p>2/ Torque your wheels!! Can't stress this enough. I had a torque wrench resident in my car. When ever the wheels were removed I personally retorqued each one in recommended pattern. (Uneven torque =warping)<p><br>I haven't had any problems yet with a4, but i have not done any real hard driving yet. I assume the calipers on the a4 are dual pistons.<br>I still am not entirely convinced of how effective the a8 upgrade is, since u still have the same swept area (area the pads cover) on the upgrade. The bigger rotor should dissipate heat better, but i just can't expect a big difference in overall breaking efficiecy (comments?)<p><br>1996 a4 2.8 qm<br>(brother has the laser now)

The s4/A8 kits all use a substantially larger disk (pir^2) for more thermal mass and a longer lever (r) arm for better braking.<p>Actual swept area is important but race pad compounding can sometimes be more effective if there is less swept area so that they heat up fast and air can pass around the pads. <p>The best solution for track use is to duct them directly and use open face wheels.

i still need to do the math to convince myself. While i know that the longer lever should make a difference, i can't belive it is significant with this small change in radius.<p>Looking at the formula 1 race brakes, the swept area is almost half the rotor!?!<p>Thermal mass: longer to heatup, also longer to cool? Aren't u looking for surface area to dissipate heat? <p>1996 a4 2.8 qm<p><br>

Ranbdall made some excellent points. From mbout 10 years of Porsche Club track events, drilled rotors can actually amplify rotor cracking, since each hole is a stress point, and the process of drilling a rotor actually induces high stress points. Slotting has been reommended over drilling on a rotor that has neither.<p>The thing that really helped my 911s was installation of brake cooling ducts. These mount under tha A-arm and have a flexible hose (like a dryer air hose) to duct air into the eye of the rotor. This amplifies the effect of the vented rotors (I assume the A4 has slotted, not solid front rotors?).<p>Might check some of the high-perf. houses.

I have the slotted rotors...<br>Soon to get the factory pads back on! On these cold (40degree) Dallas nights, I can't get the brakes up to operating temps!

Try it this way,<p>I think the stock rotors are 260 mm to fit the 15" rims, the next size is 280 mm, there is a 310mm, and the race is 330 mm. More length allows for more torque to be applied to the "axle". This is just like a breaker bar, you want the longest that fits the rim.<p>I think formula uses carbon/carbon? I'm more familiar with the brakes used in touring cars. The brake disk is huge, but the braking surface is quite narrow, 2" of the outer edge.<p>As for the mass it is, obviously, a more complicated issue. The disk has cooling passages in the middle. In racing they use the ducting I mentioned before, which has been repeated by Ray I think. They also use ducted wheels (in the front) to maximize drawing the air out from the rotor. But is is a balance of aerodynamics vs cooling. And, cooling vs. unsprung weight.<p>Yes, more mass stores more heat and cools more slowly. You want this. It is rapid heating and cooling, and clamped calipers (trapping heat in one spot) that promote warping. But, these upgrade disks also have spiral (rather than straight) internal holes which "fling" more air. They also have complicated mounting designs which virtually eliminate any stress from the bolts (not true for old, non-hat designs). <p>Fade is another issue. The caliper design plays a much bigger role in this. It is mainly heat transfer to the fluid. You need great fluid like castrol srf or dot 5.1 (NOT 5.0), and a decent caliper design. Cooling the caliper with open or ducted whhels helps this too. BTW, rally uses coolant IN the calipers (and some misting systems) to eliminate this.<p>This help?

1/ didn't know that the bigger A8 conversion rotors are spiral-cool (in more ways than one).<p>Are all the a8 conversions 1 piece rotors? i am wondering if the "Hat" designs are available.<p>Is the a4 a 2 piston or single piston caliper. I found that made a big difference as well. The pads seemed more likely to bind up (?) and be uneven in application with a single piston. I know the formula guys use multiple piston arrangements.

nt<br>

I'm doing the Alcon big brake package. The package I'm getting will be the Alcon B-type, dual piston calipers that are used by the Touring Cars. <br>-Cathleen<br>

Let me clarify!<p>I was clumsily refering to the KVR and Brembo larger diameter conversions. (do the A8's have two part numbers?) I have never seen the A8 kit. <p>I refer to the two other conversions because of the price differential (lower) and I was told by my dealer that the bearing and hub section had to be changed as well. <p>The S4 lit claims multiple pistons. Brembo and KVR<br>kits come with multiple pistons as well. They give better feel and less taper to the pads (if they are different diameters). The big difference is the weight. The kits have lightweight aluminum hats and calipers, supposedly cutting off several critical pounds to the unsprung weight.<p>The drawback is the need for bigger diameter wheels and maybe a funky offset. I'm waiting for the warranty to go off before I put the KVR's on.<br>

A few things we've run into in the last few years of building upgraded brakes packages for audis amoungst others...<p>The single biggest improvement that can be made is the clamping force being applied to the rotor. (read bigger calipers) Such as the Alcon 6 pot or 4 pot calipers. <p>The second best improvement that can be made is the lever arm. The larger the rotor diameter, the longer the lever arm, the greater the greater torque applied to the axle.<p>Cooling...while it is very important and adding cooling ducts certainly helps, cooling alone isn't the answer.<p>Swept area: the larger swept area that a rotor has, the better. Most often, a small diameter OE type rotor will have a larger swept area than an aftermarket rotor with a larger diameter. However, most aftermarket calipers are built for a standard swept area of 2". Why? Physical characteristics of the caliper. The Alcon B-Type for example, has a body length of 11.5" while the stock A4 caliper is only approx 6.5". <br>This 11.5" body has the pistons and swept area oriented on the outermost edge of the rotor, placing the pad's swept area along the arc of the rotor instead of concentrating it on one square portion of the rotor. Makes for a more effective use of pad material.<p>One note, I _think_ the A8 rotor was mentioned in another response...The A8 rotor is a 1-pc casting, just like all audi rotors. No fancy directional venting or anythin else. We use these all the time.<br>Another note, the A4/S4 that we are seeing next year uses the stock A8 rotors and A4 calipers. Increase in lever arm only, nothing else.<p>Todd C.

A few things we've run into in the last few years of building upgraded brakes packages for audis amoungst others...<p>The single biggest improvement that can be made is the clamping force being applied to the rotor. (read bigger calipers) Such as the Alcon 6 pot or 4 pot calipers. <p>The second best improvement that can be made is the lever arm. The larger the rotor diameter, the longer the lever arm, the greater the greater torque applied to the axle.<p>Cooling...while it is very important and adding cooling ducts certainly helps, cooling alone isn't the answer.<p>Swept area: the larger swept area that a rotor has, the better. Most often, a small diameter OE type rotor will have a larger swept area than an aftermarket rotor with a larger diameter. However, most aftermarket calipers are built for a standard swept area of 2". Why? Physical characteristics of the caliper. The Alcon B-Type for example, has a body length of 11.5" while the stock A4 caliper is only approx 6.5". <br>This 11.5" body has the pistons and swept area oriented on the outermost edge of the rotor, placing the pad's swept area along the arc of the rotor instead of concentrating it on one square portion of the rotor. Makes for a more effective use of pad material.<p>One note, I _think_ the A8 rotor was mentioned in another response...The A8 rotor is a 1-pc casting, just like all audi rotors. No fancy directional venting or anythin else. We use these all the time.<br>Another note, the A4/S4 that we are seeing next year uses the stock A8 rotors and A4 calipers. Increase in lever arm only, nothing else.<p>Todd C.

any idea on the cost of your proposed upgrade?<br>Going to the a8 rotors only just didn't seem to make sense to me considering the cost. I had upgraded my talon (see above) for about $1400 CDN.<p>anyone know if the a8 has dual piston calipers?<p>for $2000 i would expect dual piston calipers, and beefy pads.<p><br>1996 a4 2.8 qm (RED)<p>PS: reading the archives, and showed some friends pics of your car and said "thats what mine will look like next year" (Right :)<p>great pics!! (including the portrait :-)

Thanks for the info!<p>I was responsible for the A8 misinfo. I agree that a longer caliper is better for all the reasons we talked about, but how would a 2 vs 4 puck give more braking/clamping force? <p>If the caliper is the same size, the puck has a bigger area in the 2 vs. the 4 and the distance is the same from the pedal stroke. The smaller area pucks will travel a further distance, but the clamping force is the same if the area of the pad remains the same.<p>The braking just happens earlier in the stroke, as far as I can tell. While we used to have to change the mastercyl. diameters and the balance, now the abs takes care of that up to a point. <p>One final question: If I can lock up my brakes easily, what I really want is better modulation, not clamping force anyways. That was the real advantage for me with multipuck calipers. What are your thoughts on this?

Great car you have!<br>Thanks, I'm glad you like my changes. <br>Is that $2,000 CDN for the A8 package? The A8 caliper is a single piston caliper but is not interchangeable/bolt on to the A4 model. You can do the A8 rotors, but you have to go with caliper that has an A4 application.<br>

Being very general here... a 4 piston caliper will have more clamping force that a 2 piston because there is more pressure being applied to the pads. Also, this pressure is being applied evenly on each side of the rotor rather than on one side of the rotor as in a 2 piston caliper.<br>I agree with your statement that the surface area of the piston itself is larger in 2 piston calipers than 4, but you lost me with the line about the distance to the pedal...<br>The smaller piston will travel further, true, but the pistons travel is limited by the pad so we're really talking about velocity. The smaller diameter pistons will travel faster. i.e., less pedal travel for given piston travel.<br>If you can lock up your brakes quite easily, what you really need is a larger rotor. The larger rotor will require more clamping force due to the increased rotational mass.<p>-todd