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Originally Posted by porsche986spyder
I don't agree with that. The only thing cross drilled rottors due is keep the rotors cooler. The surface area is what counts for braking distance. And if they are bigger than the stock O.E.M. base model then it should be better. Best of all would be a set of cross Drilled & Slotted(for venting brake dust/gasses to escape) rottors for better cooling and venting. You should upgrade the pads too while your at it. 
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Cross-drilled rotors do nothing in the way of cooling. In fact, removing that material allows for an increase in heat since that space is not available for dispersing heat.
Rotors need to do two things well. First, they must disperse heat. Second, they must dissipate that heat. In addition, they must have the appropriate amount of surface area.
The mass of the rotor assists with heat dispersal. It takes much more energy to heat a large item than it does to heat a small item. As brake force is applied and things heat up, the heat is able to be distributed throughout that entire mass. If you remove some of that material, which is the case when rotors are cross-drilled, you not only have removed material that assists with dispersal (this may actually result in
increased temp) but you've also reduced your swept area (cross-drilled rotors typically have ~85% or so of the surface area that a solid/blank rotor will have – ie. 15% less).
So, decreased mass results in a lesser ability to distribute heat energy thoughout the rotor, thus making it less "efficient" at dissipating heat, which in turn results in increased rotor/pad temperatures and reduced braking performance.
In addition, there is an additional point of heat stress, which of course means it’s a risk to structural integrity. If you look at used cross-drilled rotors from a race car (this is becoming rare...not to mention they may use different materials) you may notice heat cracks originating from the holes (you’ll also notice they throw these away after just about every race...how practical is that?).
As for the swept area, the more friction that can be generated between the rotors surface and the brake pad, and greater energy transfer (stopping power) can be obtained. A smooth surface will help insure that more of the pad surface area is in contact with the rotor.
The only way a cross-drilled rotor will make a difference in overall braking is if you increase swept area and/or increase the mass to make up for the material that was removed. Again, you need to account for heat dissipation and maintain braking surface area.
So, the key to your statement is that he has to go to a larger size drilled rotor to acheive the same braking effect as a solid rotor. Unless the size of the rotors are increased, you've done nothing to improve your braking.
A few mildly interesting sources of information that relate to the topic:
http://www.thebrakeman.com/rotortech
http://www.raceshopper.com/tech.shtml#brake_performance
Also for arguments sake, take a look at these braking distances (both test results according to R&T):
'00 Porsche Boxster S - cross-drilled standard
F: 12.5 (diameter) x 1.1 (thickness)
R: 11.8 X 1.0
Braking distance
From 60 to 0- 125 ft.
From 80 to 0 - 219 ft.
'99 Porsche Boxster - solid standard
F: 11.74
R: 11.5
Braking distance
From 60 - 121
From 80 - 214
Notice that not only is there no improvement in the S' braking distance, it's slightly longer than the Boxster's, albeit only a few feet - this despite larger brakes. A couple points worth noting here: The curb weight of the Boxster is 2811 lbs., the Boxster S is 2910 lbs. There is admittedly almost a 100 lbs difference. However, the Boxster S that was tested had the larger wheel/tire package than the standard Boxster meaning it potentially had a better footprint/stopping capability.
When you get down to it, cross-drilled rotors are more about marketing than anything else.
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