From an email chain with Adam around the end of March. I was looking at SS donors at the time, so this info is for SS donors.
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""We aren't going to use the big brakes on any of our cars and don't recommend them on everyone else's cars. Since they are designed to stop a fully loaded Cobalt SS at a track, they are overkill for the Goblin. On the original P1 and P2, we use the stock rotors all the way around but when we rebuilt P1, we decided to use a rotor in between stock and SS on the front of the Goblin. We really like how it balanced out the braking front to rear.
So instead of supplying base model rotors (10.08 inch diameter) with the kit for the front of the car, we are supplying the smallest 5 bolt front rotor (11.02 inch diameter). It uses the same caliper but it is mounted further from center, increasing front brake force a little bit.
On the rear you will use stock Cobalt 10.08 rotors. With 11 on the front and 10 on the rear, you end up with a great balance without a bias adjuster. Since you don't have stock brakes to put on the rear, they will have to be purchased (you can get them cheapest from RockAuto.com:
http://www.rockauto.com/xx/cart/?cartid=0df4030809368b14ef9ae7eb7f6c79e0.
We didn't make this very clear on the website because we've been figuring out the SS stuff as we went. Now that we've figure out that extra calipers have to be purchased, custom shifter cable mounts have to be fabricated and other changes must be made, we've raised the price of the kit when using SS donors (you can see this change on our site).
On the SS cars, we are recommending the wheel bolt pattern be changed to 5x114 so that finding wheels is possible. We can redrill your rotors and change the studs in your hubs (you'll have to send your hubs to us).""
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Hope that info helps and is still correct.