1997-2003 GP catback on 04 Impala?

[Impala131]

Hey all,

Is the dual muffler catback from a GP a drop-in replacement for a single muffler catback on a Chevy Impala? Already got SD headers on the way, figure I might do the catback at the same time for looks.

I don't want to spend big bucks on a catback, I just want to spice up my Impala's exhaust a bit. Dual muffler catbacks from GP's are cheap and plentiful at the local junkyard. Dual exhaust Impala's.... not so much. I might be able to find a dual exhaust Monte here or there also, if that would be a better swap.

I don't suppose there is any performance benefit to the exhuast swap for a mild top swap build, is there? I know the GTP catback is good for anything an M90 can push out, but I wondered if the single exhaust would be any different. I'm guessing not, since it necks down to a 2.5" restriction before the split anyway. Figured I'd ask for an opinion, though.

[2004l67]

Are you in it for sound or for performance?

I'm in the midst of a motor swap, but probably going to do the zzp downpipe (mostly to eliminate the u bend) since I've already got the stocker off.

I'm considering the SD headers too while I'm there. Let me know how yours fit. I know the GP guys say you need to "massage" the firewall. Don't know if that holds true for our wimpala's or not.

[Grimsin]

I have a 05 impala with sd headers on it
Gp catback will fit but 06+ catback off a impala ss will sound better.
And yes you have a hammer back the firewall and gently bend the a/c line down out of the way. Dont get the zzp dowpipe if your getting sd headers because they have their own downpipe.
I have vids of my exhaust setup if your interested.

[Impala131]

Are you in it for sound or for performance?

I'm in the midst of a motor swap, but probably going to do the zzp downpipe (mostly to eliminate the u bend) since I've already got the stocker off.

I'm considering the SD headers too while I'm there. Let me know how yours fit. I know the GP guys say you need to "massage" the firewall. Don't know if that holds true for our wimpala's or not.

Just completed my SD header install on my 04 Impala today. As Grimsin said, an A/C line does need to be bent. That was no big deal.
As far as denting in the firewall, I didn't do much at all. The O2 sensor wires were somewhat close, but did not appear to be in danger of touching. I gave it a few whacks for good measure, but all looked good.
Also had an issue with a metal heat shield for a radiator fan getting in the way of the front manifold. I ended up clipping off one of the plastic supports for it, and bent it out of the way.
Also had some trouble getting the trans dipstick tube back in, although it may have been unnecessary to remove it in the first place. Not certain.
Also some stubborn old crossover and rear manifold bolts. Ended up cutting a few. The SD kit replaces all of those items, so no problem there.

I'd say the whole install took about 7 hours with a friend helping me. I'm sure there are pros that could have done it faster, but I feel the headers are well worth the effort. I've also installed them on a GTP with great results. You really can't go wrong for less than $200 + install items.

[Grimsin]

Make sure the trans dip stick isnt touching the headers or itll create false kr.
Same witg o2 sensor if your motor mounts are worn you engine could rock enough for the 02 sensor to hit the firwewall

[Impala131]

Make sure the trans dip stick isnt touching the headers or itll create false kr.
Same witg o2 sensor if your motor mounts are worn you engine could rock enough for the 02 sensor to hit the firwewall

Yep, good advice here. My motor mounts are brand new, maybe that's why I didn't have any issues with the O2 touching.

[blueguy]

Gp catback will fit but 06+ catback off a impala ss will sound better.

I want to know how a FWD V8 catback is any different than any of the V6 cars with dual outlet catbacks.

The mufflers are identical.

Yours only sounds different (better is a matter of opinion) because you hacked off the resonator...and headers will always change the tone of the car, too.

[Grimsin]

the mufflers are different from the 3.8l grand prix vs 3.9l and 5.3l impalas, and the catback is 2.5'' for the 3.9l and 5.3 impalas.

[blueguy]

It makes no difference.

It'll still sound poopy.

Dynomax super turbo's with catless headers (or catted...it'll make it even quieter), long glasspack...very tame note. No rasp or buzz either. I'd recommend it a million times over after hearing it in person.