New exhaust yes or no.

ls1mike wrote:
There is plenty that can be done with exhaust and intakes on EFI modern engines. Look at the Ford MOD Motors and LSX motors. My own 11 Sec 1/4 LS1 Trans Am is a good example. The difference between an LS6 intake on an LS1 is about 15 to 20 HP at the wheels without a tune.
Next you do the tune and get even more gains. The best way to do it is on the Dyno.

Now having said that a catback alone won't do it. You may see a few hp at the wheels, but you won't even notice it and you will be out at least 500 bucks.

A complete exhuast system with a tune on a modern EFI vehicle may net anywhere from 20 to 40 RWHP depending on the engine and type of exhaust system.

My WS6 gained 26 HP and 32 FT/LBS of toruqe from a custom exhaust, stock cats and mid length headers. Then with the LS6 intake I picked up another 16 hp and 13 ft/lbs of torque. All at the wheels, Dyno proven.

Problem is you have to be willing to do the whole thing. Headers, Cats, exhuast and tune. So you are looking at a pretty good chunk of money. 1200 bucks for nice headers, 300 bucks for a dyno tune and at least 600 for a complete custom exhaust. More if you get an off the shelf catback.

If you are not trying to pick up tenths in the 1/4 mile, I am not sure it is really worth it unless you like the sound.

It is why my 6.0 Chevy truck, which is really similar to the 5.7 in my WS6 is bone stock minus a tune to change the Transmission shift points and when the torque converter locks up.