Convince me to keep my second catalyic converter

[1996Battlewagon]

I'm curious as to how confused my ECU would be if I simply took the second cat off, replacing it with a straight test pipe or, of all things, a muffler (i.e. relocate of the current one).

Anyone done this?

[httrdd]

aren't your cats the ones that come after the y pipe and are they not together? Emission inspection?

[1996Battlewagon]

Emission inspection?

Nope :cool:

[Garrison]

Install a spacer on the rear 02 sensor and you can run a track-pipe without the CEL coming on.

[Guig'z]

Wich size spacer? I have CEL and emptied my second cat

[Garrison]

Enough to remove the "snout" of the 02 sensor from the flow of the exhaust stream. It helps the rear 02 sensor to be less sensitive to the changes in exhaust flow.

[ouch1011]

Assuming you don't have a California emissions car, the rear cat convertor isn't even monitored by the PCM. So you could take it off and the computer would never know. The rear O2 sensor is installed in the body of the front cat, so it is only monitoring the front cat.

[1996Battlewagon]

Assuming you don't have a California emissions car, the rear cat convertor isn't even monitored by the PCM. So you could take it off and the computer would never know. The rear O2 sensor is installed in the body of the front cat, so it is only monitoring the front cat.

Really now!?! So the ECU won't give a turkey if there is no rear O2 reading causing it to run richer than a Subaru already does?

I don't have a Cali car nor does TN have emissions testing: I might be doing this. I wonder how much louder that set up would be. And I don't really want any rasp...

[Reason]

My legacy is cali emissions, and about a year ago my second cat broke. I had a straight pipe welded in. At the time it seemed fine. I just had all other problems so it never stood out. So I guess my post is irrelevant then.

[prodriver1]

rallitech has o2 spacers but I just used a set of spark plug nonfoulers drilled one out 1/2 inch and put them together.

[prodriver1]

and for the rasp I replaced my cat with a glasspack, sounds amazing:)

[ouch1011]

Assuming you don't have a California emissions car, the rear cat convertor isn't even monitored by the PCM. So you could take it off and the computer would never know. The rear O2 sensor is installed in the body of the front cat, so it is only monitoring the front cat.

Really now!?! So the ECU won't give a turkey if there is no rear O2 reading causing it to run richer than a Subaru already does?

I don't have a Cali car nor does TN have emissions testing: I might be doing this. I wonder how much louder that set up would be. And I don't really want any rasp...

The rear O2 sensor is installed in the rear of the front cat. So, removing the rear cat doesn't change the rear O2 sensor readings because it is upstream of the rear cat. If you aren't doing anything with the front cat, leave the rear O2 sensor in there, and there should be no CEL.

Picture for reference
https://sl-i.net/FORUM/images/imported/2011/06/picsay1308025384-1.jpg

Sorry for the clutter, its been sitting on the garage floor for a while.

I can't say much for the noise, but I can say that headers with no cats on the stock catback exhaust sounds like ass when it is cold lol.

[Reason]

FYI guys not all of our O2 sensors are in the same locations. Cali spec on my 98 L the second one is after both cats. Then there's that set up pictured above. And then the 99 GTs have 3 cats. Its all wacky but that's Subaru for you!

[httrdd]

I only had 2 cats on my 2.5. Weird.

[SubieBD6]

A few months ago I got rid of the second cat and the resonator and upped the pipe size to 2 1/4" and put a flowmaster universal muffler on. About two weeks ago now the CEL came on for the o2 sensor but I haven't tried putting in a spacer for the second o2 sensor yet so I defiantly need to try that (both of my o2 sensors are on the first cat like above, I have a 98 2.5GT). As for the sound is pretty deep and damn loud, but if your getting on it and shifting at 4000+ RPM it's rather raspy how I have it set up, and it isn't like your typical Subaru rumble. But i don't have aftermarket headers either so I'm sure that would help with the raspy sound or maybe get a high flow cat, or maybe even a small resonator on there. I don't mind it too much but I'm defiantly going to switch it out probably towards the end of the summer to get that Subaru rumble, I need a CAI as well...

[Huffer]

^^ put the O2 spacer on your 2nd sensor. Not the first one.

[Reason]

I only had 2 cats on my 2.5. Weird.

Could be a cali spec or just the build dates?

[DarkPhoenix]

I have a CA Spec car (97 OBW) and rear o2 was after my second cat. I replaced both cats with one high flow unit and haven't had any CELs for cat efficiency. Misfire CELs after changing my crank sprocket and pulley on the other hand are a different story.

[SubieBD6]

^^ put the O2 spacer on your 2nd sensor. Not the first one.

Yeah, that's what i said. I just specified after that both of the o2 sensors are in my first cat to clarify that mine is not like the Cali spec. I probably just worded oddly, I'm pretty good for that. Thanks for lookin out though, I appreciate it :smt023

[1996Battlewagon]

My set up is two cats with the second o2 before the cat (I replaced both o2s 30k miles ago). I do have UEL headers with a 2.25" cat back and its soooooo deep it sounds like thunder and I don't really want to change that. I don't care if it gets louder, I just hate raspiness.

[SubieBD6]

I wish i could get a sound clip up here for ya, but my camera isn't recording sounds :smt017 But it gets pretty darn raspy without the resonator and second cat especially if it's chilly out it gets a little raspy throughout acceleration. So maybe a high flow cat to replace the second one would be better for your preference to give you more airflow and should keep it from getting that raspy sound.

[1996Battlewagon]

I got you. I might be ditching the test pipe idea then.

I have been toying with the idea of moving my muffler to the location of the second cat (getting ride of it in the process) and having the exhaust tip turn and exit out the side, right before the rear wheel.

I was going to talk to my exhaust shop to see if this is even do-able.

[ouch1011]

FYI guys not all of our O2 sensors are in the same locations. Cali spec on my 98 L the second one is after both cats. Then there's that set up pictured above. And then the 99 GTs have 3 cats. Its all wacky but that's Subaru for you!


Assuming you don't have a California emissions car, the rear cat convertor isn't even monitored by the PCM. So you could take it off and the computer would never know. The rear O2 sensor is installed in the body of the front cat, so it is only monitoring the front cat.

:smile:

The only models I've seen with 3 cats are the 6cyl models. They have 1 for each bank and then 1 right at the Y-pipe. Some models have a resonator that looks like a cat from the outside, but if you actually look inside it, its a resonator. The WRX/STI has this.

[Reason]

Yes its almost square in shape right? The 99GT I sold EvoLegacy has 3 cats.

[SubieBD6]

I have been toying with the idea of moving my muffler to the location of the second cat (getting ride of it in the process) and having the exhaust tip turn and exit out the side, right before the rear wheel.

http://www.magnaflow.com/02product/shopexd.asp?zone=main&id=9228

Maybe a muffler something like that one^^so it's small enough to fit and put it in place of your second cat and have the exhaust tip exit out the side like you want. Unless your muffler would already fit that is. I don't know if there is any room to actually tuck the piping up underneath the side but it could at least run straight out the side, if something like that would work that is.

But without at least a resonator somewhere in there wouldn't it still be raspy? You'd be getting rid of the second cat this way still.

[ouch1011]

My 98 had one too, but you could see a perforated tube running through the center of it so it was obviously a resonator. My friends STI has the same thing as well.

I'd take a pic, but my stock catback is long gone.

To the OP, I'm not sure you'll have any issues with rasp as long as you have a quality muffler. My car has headers (albeit EL ones, they tend to be less raspy than UEL) and just a single HFC, then a long resonator and straight through muffler (all Magnaflow). There is no rasp at all, its actually pretty quiet.

[1996Battlewagon]

The muffler I already have (the one I'd like to relocate) is a Vibrant Performance Street Power. Very high quality and as of right now: absolutely ZERO rasp.

That magnaflow design looks legit but I've never really been a fan of that brand to be honest.