Brake upgrades.

cross drilled or slotted rotors help dissipate the gases produced by hard braking. High tech race cars use totally different rotor and pad materials than we do and their brake systems are designed to work at very high temperatures....indeed, they don't work properly at all when they are cold. Their application does not relate to ours.
In practice, drilled or slotted rotors do offer a slight increase in braking performance over stock ones but the improvement is slight while the expense is not. They also tend to wear out quicker....both pads and rotors. As most of the brake upgrade posts here show, the Toyota 4x4 front brake mod is excellent and if you do it you will see no further improvement by modifying rear brakes. Trevor is wrong in his posting. Mass absolutely does not dissipate heat; surface area dissipates heat. That's why the quickest way to cool down a cup of coffee sitting on the table is to spill it all over! A heavier rotor will take longer to heat up but, because it's surface area is essentially the same as a lighter rotor, it will also take longer to cool down. Vented rotors cool down quicker, and using them is a good idea. Note that a vented rotor is different than a cross drilled or slotted one. Any change increasing the ratio of surface area to mass will produce a rotor that cools quicker. In addition, a lighter rotor reduces the unsprung weight of the car, improving handling and acceleration.But the improvement caused by slotting or drilling rotors is from a different source. Our brake pads produce gases as part of their ablative action and cross drilling or slotting helps dissipate these gases, preventing your pads from floating like an air hocky puck on the rotor. But, like I said, the improvement is slight.

From Grassroots Motorsports:




Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the ‘40s and ‘50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as“gassing out.” These gasses then formed a thin layer between the brake pad face and the rotor, acting as a lubricant and effectively lowering the coefficient of friction. The holes were implemented to give the gasses somewhere to go. It was an effective solution, but today’s friction materials do not exhibit the same gassing out phenomenon as the early pads. For this reason, the holes have carried over more as a design feature than a performance feature. Contrary to popular belief, they don’t lower temperatures. (In fact, by removing weight from the rotor, they can actually cause temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads—sort of like a cheesegrater rubbing against them at every stop. Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it. The one glaring exception here is in the rare situation where the rotors are so oversized that they need to be drilled like Swiss cheese. (Look at any performance motorcycle or lighter formula car, for an example.) While the issues of stress risers and brakepad wear are still present, drilling is used to reduce the mass of the parts in spite of these concerns. Remember that nothing comes for free. If these teams switched to non-drilled rotors, they would see lower operating temperatures and longer brakepad life, at the expense of higher weight. It’s all about tradeoffs. Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the brake pads over time, helping to reduce the glazing often found during high-speed use which can lower the coefficient of friction. While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut properly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)