I stopped by the exhaust shop today to plan my Y-pipe and high-flow cat upgrade. I'm planning to bump up to 3" pipe throughout. The shop says sometimes if you mess with the placement of the O2's or change pipe diameter it can cause a code.
Are there any rules to follow or things I need to do to prevent a code?

I'm thinking of these two options for install.

Preferred Option 1) Cut out factory Y, add Magnaflow Y, precat O2 bung in 3" pipe, 3" Magnaflow Cat, postcat O2 bung in 3" pipe. Any problems with this setup?

Option 2) Cut out factory Y, Downpipes come together and will fit directly to dual inlet Magnaflow Cat with O2 installed in Cat, postcat O2 bung in 3" pipe. Any problems with this? (the dual inlet is what comes up at Magnaflow)

I will try to keep placement of O2's exactly the same as where they're at now. (angle, depth, pipe length)
Will this work and keep the truck emissions legal and no codes?

 

If I am looking at the diagrams here right, the cat in your pic shouldn't work.... Don't you have a single in, single out cat? that is already installed in 3" pipe?

 

Yes, I do have a single inlet 3" Cat already, it has 164K miles on it. I want to replace with the 3" Magnaflow cat and remove all sections of 2.5" pipe. My thinking is that the Magnaflow cat will have less restriction than the aged factory one. Is that correct?

The dual inlet will fit when the stock Y is cut out because the 2" down pipes come together parallel b4 the Y.

I was reading the jegs Y-pipe thread about the non-fouler trick, guess I could do that if I end up with a code.

 

Just look for a SI/SO cat, that will mount up in the stock location. It will flow better than the stock unit, and give you a bit of a power nudge.

 

Okay, SI/SO is what I'm planning. I'll update when done.

 

if you're going through all of that I'd be danged if I wouldn't get rid of that factory Y.. it is a ridiculous thing, and likely the cause of the lions share of backpressure.

 

Factory Y changed for model year 2000. Much better than the piece of crap on the older trucks.

 

Mine's an '02.. I cut the thing open and looked at it.. if it was an improvement, my god, the previous ones must have been drinking straws...

 

hey drew, didn't you have some pictures of a cut open y off your truck?

 

I didn't take pictures of that thing.. and I regret it hugely..

the dude who welded up my exhaust (welding is akin to alchemy to me) was doing his thing, and I had a cutting torch and a cutting wheel- so I did what I did while he did what did.. and that Y got opened up..

imagine a drinking straw.. now imagine another approaching the first one at about a 60 degree angle.. now imagine taking yet another drinking straw, and cramming the first two into it.. that's pretty much what my Y pipe accomplished.. instead of being 2- 2.25 pipes from the collector joining in a well formed 2.25" or 2.5" pipe, it was two 2.25" pipes that had been crushed to somewhere around 1.5".. the other side of the Y was 2.5" and fed the cat within inches- compounding the issue..

that dang thing sucks donkey donuts..