I have a set of ASM Long Tube Headers (although one side seems longer than the other ) and a Magnaflow cat back so far.

Since I'd have to cut up my stock y-pipe to get the headers to fit I was thinking about getting a new y-pipe welded up instead. That way when it came time to smog the truck and if I couldn't find a "hook up" I could just swap back to stock manifolds and y-pipe. No damage done.

So here's the question, when I go to get this done at a muffler shop do I run new highflow cats? do I just run straight pipes? will one work better than the other (i.e. throughing codes) things like that.

what are the pros and cons and your recommendations?

 

If you remove your cats, it will throw codes, but you can remedy that with either a set of o2 sims for your rear 2 o2 sensors or if you have edit you can delete them that way. From what I've heard, the stock cats flow pretty well so I don't see too much reason to replace them with aftermarket ones. Just my .02

 

04 Sierra, the reason I would replace them is because my ASM headers are not CARB approved and if I couldn't find a smog shop to overlook that I would have to put the stock manifolds back on to pass. But if I hacked up the stock Y-pipe(with cats) I would be SOL as well because 1. the stock manifold would no longer bolt up and 2. the visual would be altered do to the hacking of the stock Y-pipe.

Sooooo

I'm trying to plan for worst case scenario. i.e. no smog shop "hookup".

In that case I would need to keep my stock Y-pipe and exhaust manifold intact.

the question is what do I do as far as exhaust equipment/routing from the header collector to the muffler to through no codes and still be able to pass a smog test if I had a "hookup on the visual.

can you help me out with that?

 

I made up new front pipes without cats for my ASM headers. I saved my front pipes without cutting them up. Then it will be very easy to go back to a stock exhaust.

If you don't mind paying a little extra, go for it. On my Z71, I used a flowmaster Y-collector 2.5 dual in, single 3" out.

 

04 Sierra,
I got an 04 Sierra EC/SB in December & haven't done anything to it yet. Been reading posts on here & sounds like Corla or Magnaflow cat backs are the best. How do you like your Mag & Volant? Had a 99 Chevy EC/SB with the 6.0 previously. Put a Dynomax 2 in & 2 out on it since the 6.0 came with 2 cats & separate pipes going into the "trash can" GM calls a muffler. So I had pretty close to a "true duals" system. Impressive results--2 MPG (9.5 MPG to 11.5 MPG). Felt a power difference too, especially pulling my boat. But, it was very loud--especially the droning on the highway. New truck has averaged 16+ MPG over the first 6K miles. Not sure how far I'll go with mods, but would like exaust mod that provides some MPG & power bennies, but would also like it to be quiet on long highway runs. Appreciate any help!
Thanks, Scott

 

BigTex, looks like I'll have a similiar set up, I ended up getting the magnaflow daul in/ single out.

When you went to no cats w/ your custom mid pipes did that give you any problems?
if so, what did you do to clear them up?

 

I unhooked the rear O2 sensors and left them on the stock pipe. I used my LS1 Edit to turn off the sensors. You could do the same thing if you have custom tuning, or buy some O2 simulators which fake the signals to the computer.

 

where could I buy O2 simulators?

 

Thunder Racing sells.

 

much thanks!