NickWayne100

I've searched and searched for information regarding this and couldn't find a single post about it. I'm building a new exhaust setup for my 1999 trans am with a stock LS1.

My goals: Replace stock manifolds and Y-pipe with the BBK longtube + Y-pipe package (Non catted Y). I want to install an electric cutout followed by a single magnaflow cat on the I-pipe so that i can switch between open header mode and cat+muffler mode.

My concern is, can i still pass emissions with a single cat on the i-pipe rather than dual cats on the Y. (I live in Texas). I would buy the biggest converter magnaflow sells, rated to handle a 7.8L.

Has anyone ever tried anything like this? Anyone think i can pass emissions with this setup and the cutout closed?

demonspeed

iTrader: (7)

Very interesting idea! I'm definitely interested to see how this might end up playing out. It'd be a much more affordable proposition for anyone who needs converters for inspection. I can almost guarantee that the tech doing emissions inspections wouldn't have any idea that the location isn't factory. If they question you, just bring in a picture of a third gen exhaust

Majestic9C1

iTrader: (19)

that actually sounds interesting.. you would just need to have an O2 bung welded in after the cat and use a corvette sensor with the 4 or 5 foot long harness to reach the plug.

99Bluz28

iTrader: (35)

First off the cat converter will be to far away from the engine to get hot enough to work effectively, if you're just trying to visually pass by having a catalytic converter then buy a small (cheapest you can find) bullet cat, and knock all of the convert brick out of it and install it right off the end of the BBK y-pipe. Now if it does need to pass sniffer test, you're S.O.L. !
If you do want one that will still be somewhat effective then install a magnaflow # 59959 right off the bbk y-pipe and then into a E-cutout exit.. Now if you want a little better flow the you'll need to replace the bbk y-pipe merger with one that has a larger 3.5" outlet, then install a magnaflow #59920 which has 3.5" inlet/outlet, followed by a 3.5" E-cutout into a 3.5" to 3" reducer going back into the cat-back before the over-axle pipe. FYI the single cat won't reduce the overall loudness a lot, but it will give the exhaust a better sound.

99Bluz28

iTrader: (35)

WHY....?
Why would you even want to consider doing that ?
Adding a rear O2 sensor behind a converter that's to far back is only going to set a code, since it won't be able to get hot enough to be 100% effective at converting harmful compounds to harmless. So, spending the time and money to install a rear O2 is only going to tell you what you already know.
FYI, it's the same reason that the rear O2 sensor are removed(or disconnected) and either tuned out or replaced with O2 Sims when L.T. headers are installed; converter inefficiency.

BubaGumpShrimp

iTrader: (1)

the AFR is not controlled by the after cat o2 sensor,, the after cat o2 is only to verify the cat is working properly

demonspeed

iTrader: (7)

MadFirehawk86

iTrader: (2)

I have this exact setup on my car. Longtubes with an offroad Y and 1 cat in the I pipe just after the Y pipe. It works just fine. The cat is a Magnaflow high flow cat.

99Bluz28

iTrader: (35)

Yes, you're correct!
Thanks for the correction!
I'll delete the incorrect info.

98redSS

iTrader: (2)

Did you notice a difference in sound with this setup vs. both cats?

toadzq8

iTrader: (43)

I have done the same thing, I installed a 3.5" 200 cell cat in the I pipe merge. I did a run test then dropped the pipe and checked the temp of the cat element, I read 1000 degrees. it only takes 400-600 degrees for a cat to light off or start working, so it can work that far down stream, not as well but it will work, the single cat was a bit louder that the two cat in the normal position. I have a y-pipe I build with race merge and removal inserts so I can swap out diff setups.

MadFirehawk86

iTrader: (2)

I wouldnt know because it had true duals. I have a Magnaflow cat back and it is quiet at idle but when you get on it it has a nice aggressive sound.

NickWayne100

Wow I'm really surprised that some people have already done this. Setup looks great toadzq8. Like I said if it weren't for emissions I would've already done this. Have you guys been able to pass inspection with that setup? This car will be my daily driver.

5.7stroker

iTrader: (36)

Bringing this back from the dead.

I'm running:

Pace Setter Coated LT's
Pace Setter Y PS82-1163 and IZM993-2 O2 sensors, with dual DMH cutouts on the Y-pipe
Magnaflow 14419 muffler used inline with I pipe
Walker 54064 (I-pipe)
Walker 53061 (I-pipe)
CME Exhaust tips and elbows
Dynomax, Ultra Flo Welded, muffler #17227

I'm considering putting in a high flow cat 59959 before the 14419. Would this help with exhaust fumes when I have the cutouts closed, or is it not even worth the effort?