Impala Exhaust Question-single to dual?

This has to do with a 2005 Impala 9C1(cop car package) with a series II NA 3.8 with the u-bend in a single outlet exhaust. This car is a friend of mine and seems convinced that he will gain power from putting on a cat back dual set up. My question is will he gain any power? Is his exhaust similar in that his will flow and lose no power up until 350whp mark just like on the grand prix's? He plans on the following mods: HV3 PCM Plog DP and KandN CAI. Will he lose anything on his current exhaust or is the cat back worth it for him with those mods installed?

i say put the duals on it and dont go much bigger exhaust piping or leave the stock size on it. definitley get rid of the ubend

IMHO, after all those other mods are done then put on a cat back.

a catback doesnt make power. it will look better, but it wont make any power. he does know that the exhaust is single until the back end of it, right?

Originally Posted by Bio248

a catback doesnt make power. it will look better, but it wont make any power. he does know that the exhaust is single until the back end of it, right?

yeah we have a fake dual (appearance only) they are still single exhaust cars i say do it for looks but do the perf. mods.

his contention is that it will flow better with the dual outlet vs. his current single outlet. I was trying to tell him that it was a looks mod and not a performance mod. True or false? Does the impala single exhaust flow as well as the W body(GTP) dual?

Originally Posted by Bio248

a catback doesnt make power. it will look better, but it wont make any power. he does know that the exhaust is single until the back end of it, right?

do you mean on our cars, any catback he would buy, or both?

the exhaust is JUST like ours. its single to the back and then splits again. its a looks only mod. actually, a single exhaust probably flows better since its a straight shot.