LS Swap Exhaust Question

[skyphix]

I went through most of the threads related to exhaust that I could find, and didn't find an answer here...

I had planned on using sections of the Y pipe off my donor vehicle (2006 Yukon) but the Cats are too close to the O2 bung to cut off and leave enough for me to comfortably attach more pipe to complete the downpipe...

So before I throw the towel in and just run cats for the time being, or go out and spend a lot of money on a cat-less Y pipe that I am just going to cut up and use a little bit of, does anyone else have any suggestions? I'm not confident enough in my welding ability to buy flanges and build the downpipes myself, especially ahead of the O2 sensors. I'll do some welding and some clamps for the rest of it. This is fairly temporary - knowing that down the road I'll have a shop build a good exhaust. This is just to get me driving this fall for a month or two before salt and snow take over.

[MDPotter]

Are you trying to reuse the donor cats? Also, pictures help a lot.

[skyphix]

Originally Posted by MDPotter

Are you trying to reuse the donor cats? Also, pictures help a lot.

I'm actually trying to NOT use any cats at all, just trying to keep this iteration of the exhaust as cheap as possible since its mostly just to test for whats remaining of this season.

I COULD cut the stock Yukon Y pipe AFTER the cats and just run the cats for now, which is probably the simplest solution... I was just trying to not run any cats at all since its not required in a vehicle this age in my state. I can take some photos if its not pouring when I get home. I think I'll be under there anyway. The flare from the Y pipe cat on the Yukon is basically right up against the weld for the O2 bung after the flange so I can't really effectively cut there and end up with enough metal for anything other than a butt weld which I am not exactly proficient with at this particular moment especially on thin exhaust tubing.

[loosenutz]

On my previous LS swap (into a 66 Chevy II) I deleted the cats. Now I'd wish I hadn't. The exhaust smell can get pretty bad at times and I may consider putting some on now. The plus to leaving the cats on is also that they quiet the exhaust enough that you can often get away with running no muffler. I'm currently doing an LS swap into my C10 and will be using the Y pipe and cats from the donor vehicle

[MDPotter]

Do you have access to a mig welder? I don't know what your manifolds and downpipes look like, but parts stores have bends, clamps, mufflers, and hangers and you might be able to piece something together with minimal welding as a temporary setup. Or you might be better off to take it to a shop for a cheap setup that doesn't have to run the full length of the truck. Having the mufflers under the cab will give you more noise and fumes, but if it's temporary it's not a big deal. I ran my truck like that for a few months and it was fine, but I didn't drive it very often. Turbo mufflers on an LS engine without cats aren't that loud and they're cheap.

[skyphix]

Thanks to both of you. I do have access to a simple Fluxcore setup and will be using it in combination with parts store bends and clamps to connect the LS to my existing exhaust (which is a cobbled together single into dual with a summit chambered muffler) - I'll likely wind up just cutting the y pipe after the cats and reusing the Y piece to connect to my existing single pipe for now. It's really a temporary solution and I'll be daily driving this so I'm sure the non-car people at school when I drop the kids off in the morning will complain less if it doesn't smell like raw fuel. I plan on doing headers and having a full dual 3" built for me next year in prep for a built LS yet to come anyway so this is really just for a couple months. I won't be driving it much at all once they start salting the roads.

I just wanted to make sure I wasn't missing some easy solution to no cats. The hot rodder in me wants max flow but it's silly when the rest of the exhaust is cobbled together and undersized anyway.

Thanks again

[LeesTruk]

You can cobble up a Y-pipe using the exhaust stubs instead of trying to salvage the existing cats. If you're not too sure of your welding skills, just tack it together and have a welder finish it for you. I made mine from 2 1/2" pipe into the collector, and 3" out to a single muffler/tail pipe

[skyphix]

Originally Posted by LeesTruk

You can cobble up a Y-pipe using the exhaust stubs instead of trying to salvage the existing cats. If you're not too sure of your welding skills, just tack it together and have a welder finish it for you. I made mine from 2 1/2" pipe into the collector, and 3" out to a single muffler/tail pipe

That was exactly my plan, I think maybe even inspired by your truck actually. It looks like you had more distance between the o2 bungs and the cats. On mine the cat is right up against the bung. Unfortunately it was dark when I got home last night so I couldn't get any photos to explain what I was trying to say.

I figured I'd try fully welding it and if I screwed up bad enough, have one of the local guys from the track weld it up for me.

[LeesTruk]

If you do decide to fabricate a Y pipe, be sure to take out the sensors, 'cause you'll render them useless if you don't. Ask me how I know...

[skyphix]

Originally Posted by LeesTruk

If you do decide to fabricate a Y pipe, be sure to take out the sensors, 'cause you'll render them useless if you don't. Ask me how I know...

Thats a bummer. I know O2 sensors are pretty sensitive. I actually have 2 brand new ones to install anyway. I figured when I ordered my harness from PSI I'd just get the O2's they sell to avoid any issue with the wrong plugs or anything, plus the ones in the Yukon have 220k miles on them (engine only has 80k... but the rest of it is BEAT.)

But I'll still remove the ones installed so I can keep them as spares assuming they have the right plugs. Good tip there.