There's a guy around here who has one, and he's running 12.8's with no mods at all. GM underrated the new LS1 Camaro's/Firebirds so they don't take sales away from the Corvette.
Take a look on some of the LS1 forums, the new LS1 Camaros and TAs are putting out 305-310 hp at the rear wheels. Which equates to around 360 Hp at the crank.