After my second day at the track, I noticed that all the cross drill holes in the rotors were clogged with brake dust. I took an allen wrench that fits through the holes, and cleaned them all out. Was that work necessary? Do they still do what they are supposed to do if they are plugged with brake pad dust?

 

I got this issue as well and it basically renders the holes useless. Not sure it is a real issue with modern brake pads and systems (degassing and cooling) but certainly not a good thing either. I burnt a full set of OEM brakes (pads and rotors) in 3 track days. I can not say it is because of the holes being filled, but it probably did not help.
I am upgrading to 380mm Brembo BBK's with slotted rotors...

 

Cleaning out the holes helps. Every little bit of cooling can help maintain brakes. If you plan on tracking a lot, though, you may want to invest in some regular slotted rotors.

 

Yes, the holes need to be periodically cleaned out. When plugged, the rotors cannot effectively dissipate heat which leads to premature wear in both the pads and rotors. Brake fluid temps also rise which can possibly induce fade. If they are really plugged up, you can carefully use a small power drill bit. I'm not sure I'd try this on PCCB rotors however. Best,

 

How much $$$?....

 

I am usually able to clean out all the holes with my pressure washer each time I wash the car. Certainly much faster than doing it one hole at a time.

 

About the price of PCCB's for both axles (at build time, not he $20k!!!!! Porsche would charge for a retrofit). This made me ask myself if I should have gone for PCCB in the first place, but ceramic rotors are so fragile that I would have been afraid to crack them when swapping wheels for instance and they cost an arm and a leg to replace.

Back to the holes issue, they fill surprisingly fast and it is not easy to clean them between two track sessions when the brakes are burning hot. I still feel there is a design flaw somewhere.

 

The reason for the holes is not brake cooling. They are there to dissipate steam when braking in the rain. Wet brakes, when applied, do not stop well until the water on them is turned to steam and eliminated. In racing this is less than a second but Porsche and other high performance cars don't neglect this small delay.

Brake cooling is accomplished by the spiraling shape between the disc halves "fanning" the discs. All modern brakes have this internal cooling built into their shape, but only advanced or high performance brakes have the holes (or, in some instances slots). The reason for that is that drilling those holes used to weaken the discs and until technology solved that problem they were not used.

No doubt, there is probably some cooling afforded by the holes, but that was not their primary purpose.

 

Right. Which is why some recommended using slotted rotors (because the major cooling comes from vanes in the center of the rotor, while the gases that build up between the pad and rotor are dissipated through the slots (or other method)).

I think we have over engineered this.

 

Why not use air to clean the rotors...a few hits with a compressor does the trick. If you don't have a compressor, try using the canned air people use to clean electronics.

 

Well, I can tell you mine were packed with brake crap, and I had to turn the allen key around in each hole to break the stuff apart. Air might work if you stay on top of it better than I did....