GAS-SLOTTED ROTORS

Gas slots in the rotor face have several advantages over cross-drilled holes:

1. Since brakes are essentially heat-sinks, the more mass you have the better you are. Bigger IS better. When you drill a rotor full of holes, you remove quite a bit of material, and drop the surface area under the pad. This places greater heat stress on what's left, and this is one of the reasons why cross-drilled rotors tend to warp so fast. While there is an increase in COOLING surface area, this is overshadowed by the other factors.

2. Since the internal webbing is only drilled through occasionally, it is usually necessary to re-balance the assembly. Gas slots are only .050" deep, and there are only three grooves per side. Significantly less mass is removed, preserving the brakes' ability to absorb heat. This is especially helpful for autocrosses and driver's schools where rotor warping is common.

3. The entire pad is swept as the groove passes, as opposed to only where the holes would pass. This greatly enhances wet weather performance, and allows removal of the brake backing plates, almost doubling the airflow to the rotors.

4. Because the slots do not go all the way through the rotor, the structural integrity is much greater, and in fact approaches a stock rotor.

5. The depth of the groove makes an excellent visual wear indicator. When the rotors are worn to the point that the grooves are almost gone, it's time for new rotors!

6. I sell gas-slotted rotors! :) Yes, I have a bias in this field. But as a driving instructor for the BMW CCA, Porsche, Viper, Ferrari and RX-7 clubs, I have warped more than my fair share of rotors in my life. It has taken me awhile to develop a system to avoid further financial injury due to excessive rotor wear, and the gas slots ARE better. But there are a few other things you can do to help:

   • In addition to gas-slotting, if track use is expected, Berlinetta* or equivalent rotor hats are recommended. These fit over the front of the rotor and re-direct air from the hub through the internal vents.

   • I already mentioned removing the backing plates or at least fill them with holes like this:

     

   • Add air ducts that direct air onto the rotors. These can replace your fog lights, or can be mounted under the car. Just be aware of ground clearance.

   • For the truly brake-addicted, add water cooling. I fog water into the back side of the rotors which have the aforementioned rotor hats with a separate windshield washer motor. This pump runs continuously on the track. With these simple modifications you can vastly increase your stock brake's performance without spending huge money.

If you have any further questions, call Jeff @ 317-506-7314. I have in stock many sets of OEM BMW rotors, or I can slot your own new or nearly-new ones for $35.00 each. Visa/MC and Paypal gladly accepted. A set of four rotors range from $250 for '84-'91 3 series or $400 for '88-'91 M3's, to a bunch for custom 911 Turbo or E39 M5 sets. Call or email for specific applications.