Bill,

You're right about the drilling to help relieve the layer of gas that develops, that was another reason for putting the holes through.

As far as the heat capacity of the material, yes, you lose some. However, I've done enough engineering analyses to know that the amount of material you lose by drilling is probably neglidgable.

I was referring to the increased convection of having the holes through the disc. How much more? I have no idea, but as I understood it, that was the reason for claiming less brake fade.

Ideally, you would want more of the energy in braking to go into the air through convection than into the rotor's heat capacity (becasue all of that energy will have to be either convected out anyway or conduct into the caliper and brake lines), but without heat capacity, the same energy results in higher temperatures of the disc and caliper, and you're right back where you started from.

A question a lot of people ask about these is "If they're no good, then why does Porsche put them on their cars?"

I think the reason is that Porsche has done the real engineering thermal analysis to show that the pros outweigh the cons, at least with the rotors that they put on their cars. Weather or not Zimmerman or any other company has done the same analysis or is just banking on the bling factor, I don't know, and probably won't ever be allowed to find out. But for the price difference and the fact that labor is free, I thought I would give them a try. So far they seem the same to me.