headers are worth it, mine with the mods you list and headers put down 335 rwhp on a hub dyno. With a tune on top after you got all your mods done will net you some good gains.

mezzyshredder, do you know of a particular BOLT-ON camaro that makes 400 hp ?? Sounds hard to me, you need at least another cam to get 400+

 

No you don't need a cam. A full slp exhaust from headers back with no cat alone will net 40 bhp, then add porting and polishing of the heads and intake, injectors, maf sensor, ram air, and a few other mods and a detailed retune. Pretty standard at slp in Nj to get 400 bhp. I see it ALL the time

 

Absolutely I certainly do. All day

 

it is possible for a FULL bolt on (including underdrive pulley, electric water pump, etc) ls1 and a good tune to get close to 400 bhp, but adding just headers and exhaust will not net 40 hp. The catbacks are not that restrictive on fbodies and aftermarket catbacks don't net much more than a few hp. Longtubes and ORY may free up around 10 rwhp or so. Generally full exhaust ls1's with a tune will put down around 340 rwhp on post 2001 fbodies (ls6 intake).

 

are we talking 400 flywheel BHP, cause i'm sure even considering losses there is no way bolt on will get 400 rwhp?

mine was pretty much full bolt ons , headers, no cats etc, but no underdrive pulley or electric waterpump. And that was the 335 rwhp, so pretty much as you saif Failedd Devices . So Maybe about 370-380 after losses though auto box (unlocked) and error in dyno +/- 10 or so?

porting and polishing of heads are NOT bolt ons this is top end work.

Either way OP you should get some headers, more power and sound awesome