Originally Posted by jaje
i've been reading up that this all depends on the brake system...it is easier to focus more air through a system that creates a vacuum (reading up on f1 brakes the rotors are designed to create a vacuum like a compressor wheel on a turbo charger...by creating a vacuum its ducting runs through a system designed to pull air through decreasing braking temps)...basically a ram air effect with a compressor forcing even more air through it
on a normal economy car with stock brakes the dust shield impedes air flow (and heats up retaining heat in the system) even with ducting b/c you are trying to force air into a system that does not dispell it easily (no vacuum)...removing the shield and running a duct to the rotor seems to be the best method
my stock rotors are like that. basically it's directional and when installed correctly it looks wrong but it's right. with vanes should curve towards the back of the car not front of the car.
maybe you can also try cutting the leading edge of the dust shield and make a funnel like shape. I think the NSX has a similar deal stock and Dali Racing makes a mega phone sized one.
Found the pic:
