how many vents in a Cobra rotor???

Self-drilling your own crossdrilled rotors can lead to many problems. Unless done correctly, drilling holes can stress the rotor in such a way that it will crack very easily.

Also, drilling the holes will decrease the mass of the rotor creating more heat which will lead back to problem number 1....cracking.

Any drilling of holes must be done with a liquid cooled drill on it's slowest speed. Heat generated must be kept to a minimum and you should chamfer the holes whel done to decrease stress slightly.

Good luck.

Depends on what brand rotor you use.

Not all will be the same. The vents of the 94-98 Cobra rotors are not the same as the vents on the 99+ Brembo Cobra rotor. Aftermarket rotors are different as well. It's not exactly standardized. Some factory rotors may be vaned directionally while others are straight so you could use them on either side.

Kilgore Trout said:

Good rotors have the holes cast into them and are never drilled.

Click to expand...

Actually many aftermarket companies and some reputable companies machine the drilled holes into their rotors after they are cast. Brembo does it as well. The difference is the better quality companies have more controlled environments when the rotors are drilled and do not alter the metal properties of the steel when it is done. Companies like Baer and Brembo have the benefit of testing their rotors to see if they have been compromised at all and can alter their machining methods. Also, the rotors must be balanced after the drilling...which isn't something easliy done. The reason drilled rotors tend to crack a lot is due to the drilling in areas which makes the rotor structurally weaker and heat generated during the drilling which makes the surrounding metal brittle and weaker. Pretty much ALL of the cheapo cross-drilled rotors on EBay are solid rotors that have been machined. There is even one company purchasing Brembo rotors and machining them themselves and selling them under the Brembo name.

Now while 99% of these rotors will generally never fail, i still wouldn't attempt it.