160mph in a Valiant has to take some seriously large brass ones. Even with the way that car is set up, you have to be working pretty hard against the aerodynamics of the car at that point.
Yup. If the rotors are cast that way it's quite a bit different than if they've been drilled or machined. Even if they were cast that way and then cleaned up during the machining process it makes a difference. And of course, I've seen some "shade-tree" cross drilling done by folks at home that was so frightening it would give all drilled rotors a bad name.
It's all about the manufacturing. I've had the drilled/slotted 11.75" rotors on my Challenger for well over 50k miles now. I've worn through a set of semi-metallic pads in that time, and the rotors still look great. No cracking, no warping. Granted, that's on a car that's street driven, and while I have been known to get a little spirited when I take the car out to the twisty's up in the mountains, I haven't competed with it on the track. So the heat cycling I've subjected mine to isn't exactly the worst case scenario. But that's also just with regular old Summit rotors straight off the boat from China. So, not exactly the pinnacle of manufacturing or design. But the holes were cast in.
As far as your example of the engineer being over-ruled, it suggests that no engineer would ever endorse drilled or slotted rotors. Since they're frequently used on race cars that are never marketed to the public and whose sole purpose is performance, your logic is flawed. As I already said, it's all about the manufacturing. And while I know that the major auto-manufacturers are no saints, the process for getting a car through testing and out on the market would prohibit a production car getting a redesign like drilled rotors without at least the sign-off from a high ranking engineer. Maybe it wouldn't trigger a complete redesign, but you'd better believe an engineer signed off on it.
Simply saying "all holes are bad" is a pretty simplistic statement. Sure, thermal cycling can cause issues, and stress risers can be a problem (although that's more relevant to drilled holes than cast ones). But there's a lot more to it than that, and there are ways to deal with/minimize those stresses (like putting a countersink relief on the holes as revhondo suggested). Everything is a trade off when it comes to engineering design. And of course you're right about marketing/accounting and production. A lot of really great designs have been turned into disastrous products by bean counters. But that also doesn't mean that every drilled/slotted rotor on the market is a time bomb waiting to go off. The drilled/slotted rotors on my Challenger are going to run out of spec on their thickness tolerance without ever having cracked or warped, and they're far from the high end of rotor design.
