Just wondering, Would i have to worry about any problems if i went ahead and installed a header and downpipe with HF cat? any problems running to lean/rich or anything like that? i dont want to go too heavy in mods till theres some sort of tuning but my car will be sitting over winter so i was going to order some parts to be installed this winter. thanks guys

Current mods: Injen SR and DC sport catback

 

Free bump I would like to know too.

 

You shouldnt have any problems at all as long as you keep your rear 02 sensor. Otherwise you wont have problems running lean/rich.

 

does anybody make DPs that re 2.25? would like to match my dc sport exhaust.

 

i think cobalt-addiction has one

 

wut year cobalt you got. there header will not work wit the balt w/ EGR. but the DP would be ncie. they do make a 2.5" DP. check out there site

 

I have an 06 and it doesnt have egr so They all dont have it.

 

i have a 05 not sure what EGR is, i would like the GMPP header and maybe custom make a downpipe thats 2.5 down to 2.25 to match my exhaust.

 

I don't think that would be needed. The whole point of a smaller exhaust is to maintain exhaust velocity. The cat is the most restrictive part, even a high flow cat. The 2.5" b-pipe will ease the flow of gasses through this restriction better than a 2.25" would. You would not lose any exhaust velocity, in fact, it should increase the velocity over the 2.25" pipe. That's why no one makes them, only 2.5" and 3".

The 2.5" XTC B-pipe that I have bolted up to the 2.25' outlet on my CA header perfectly.
It would bolt to your GMPP manifold just as well. By the way, did you know that the GMPP manifold narrows down to about 1.75" at its most restrictive part before opening back up to 2.25"?

 

WE DO NOT HAVE EGR

Its secondary air injection and only the last few cobalts made in 2006 of the 06 model have it.