My slotted discs say never to turn them. I guess the slots are supposed to keep them from warping, so if they do warp a little then they are garbage.

I didn't know you were supposed to have brand new OEM discs turned. Is that true for all vehicles?

 

Ok I'll bite, they do? Never herd that. Power slot rotors or anybodies sloted rotors were made for 1 better pad to rotor contact 2 to let the gases that are produced from brakeing excape 3 this also allows the assmbly to keep its cool!

 

Isn't it the built up heat that warps the rotors?
...so by keeping things cool they are helping to prevent warping...

Anyway, I bought some slotted, so I'll put them on no matter what they are meant to do. The money is spent.

 

Heat is usually the main contributor to warpage...poor quality of metal in the rotor is also another contributor. Cheapo rotors always seem to warp faster. I've never heard of having to turn new rotors...this would cut down on the metal thickness before they're even used...doh! Where I work we always toss the new ones in the parts washer to cut all the oil that they ship them in, scuff them with a rotor stone, and then install them. New pads/rotors always take a few miles to break in.
Now on slotted/drilled rotors. The slots/holes are for letting the gas escape inbetween the pads and the rotor surface. When you get your brakes smokin hot gas will build up and no matter how hard you push, you cannot make the pad contact the rotor, hence the slots or holes. The fins in the middle of the rotor are actually what help the best as far as keeping the rotor cool. Directional fins are better. And if you're really worried about heat build up, get rid of the dust shield, run heat ducts, and run rims that have big openings to help keep them cool. Never a good idea to turn slotted or drilled rotors.
Hope this helps,
Gary