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I had the pleasure of being at an event with a manufacturers rep. Casting with the hole does 2 things. It reduces machining time, and tool wear, while increasing the edge strength that improves resistance to edge cracking.
The hole idea of cross drilling is to improve heat transfer out of the disc pad and rotor. Heat radiates until it hits an edge and builds up there. The internal fin force air out the hole improving surface cooling. With out the cross drilled holes all you do is cool the core of the rotor. With the cross drilled hole you cool the core and the friction surface. If you've ever watched the thermal imaging of a solid rotor versus a Cross drilled rotor it is impressive how fast the edges of the holes get hot and how fast they cool back down. While the solid one just linger hot and gradually increase overall temperature with repeated braking. I saw a side by side thermal test for 3 minutes. Braking for 5 second cooling for 15 seconds designed to simulate track conditions. the solid rotor was over 150 degrees hotter at the end of 3 minutes with a 22% loose of braking force.
My opinion would be, If the car is a daily drive then use solid rotors. If you track the car at all use drilled or drilled and slotted rotors.
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2003 Black 986. modified for Advanced level HPDE and open track days.
* 3.6L LN block, 06 heads, Carrillo H rods, IDP with 987 intake, Oil mods, LN IMS. * Spec II Clutch, 3.2L S Spec P-P FW. * D2 shocks, GT3 arms & and links, Spacers front and rear * Weight reduced, No carpet, AC deleted, Remote PS pump, PS pump deleted. Recaro Pole position seats, Brey crouse ext. 5 point harness, NHP sport exhaust
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