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View Full Version : Do I need my rear cat?


rudgers73
05-31-2009, 09:57 PM
I had some work done at the dealer last week and they noticed that my rear cat has a crack in it. Do I need the rear cat to prevent CELs? I haven't gotten under to check, but I doubt there are any O2 sensors behind it. Anyone else do something with their rear cat? I am thinking of piping through it if it isn't really necessary for emissions. It would free things up a little right?

99 Legacy GT
decke48
05-31-2009, 10:34 PM
as long as there is not o2 behind the rear cat, your car will never know its missing
rudgers73
06-01-2009, 06:10 AM
That's what I was thinking. But the only thing holding me back from doing it is that I never hear anyone say anything about doing it. How good or bad can it be if nobody talks about it? How much function can it really have if it doesn't need to be there? It seems like a $200 part that doesn't need to be there would be a "hot topic" for people that mod their Subaru, wouldn't it?
Huffer
06-01-2009, 09:32 AM
This should answer your question:
https://sl-i.net/FORUM/images/imported/2009/05/STiaxlebackmidpipe1-1.jpg
decke48
06-01-2009, 02:21 PM
you dont gain much by going catless on cars unless you have mild built engine.. i hollowed out my rear cat (since it was rattling) you only really gain sound
rudgers73
06-01-2009, 04:17 PM
Huffer: I guess pictures speak louder than words haha

Did you fab that yourself? How raspy does it make the car sound? I don't want a bunch of rasp.
rudgers73
06-01-2009, 04:21 PM
decke48: Yeah, I know I wont gain HP, but I am attracted to the idea of not replacing a $200 part and replacing it with something that will never cost $200 again.

Nobody here would happen to have dimensions or prints for that replacement pipe would they? I am assuming it isn't an aftermarket part...? Huffer?
Huffer
06-01-2009, 04:28 PM
It's a very easy job - take the car to any muffler/exhaust shop, tell them you need a new pipe between the axleback and your cats, argue with them over the 3rd cat for a few minutes, wait a couple of hours and drive away.

Stock pipe is about 1.8" ID, my "STi" pipe is closer to 2.25" ID. It was a custom fab job that cost about $80 + $30 labor.

You *can* have a resonator installed to cut down on cabin drone, but I didn't find anything significant going on in the cabin.
ScaryFatKidGT
06-18-2009, 12:40 AM
I loled at that pic

huffer you have an STi axle back?!?!
Huffer
06-18-2009, 07:54 AM
huffer you have an STi axle back?!?!

Yep.
ScaryFatKidGT
06-19-2009, 03:50 PM
do you have any sound clips? I have an STi cat-back im going to get put on as soon as I get some UEL headers.

urs is just UEL headers, 1 cat and strait piped? I have the cat-back so it has a little resenator but a bunch of people told me they sounded like crap on NA cars, I was thinking about getting a larger resenator installed but you seem to think urs sounds pretty good with out any resenator?
Huffer
06-19-2009, 04:54 PM
I might take a sound clip this weekend... but none yet. It sounds pretty nice at idle, a nice burble. WOT it's loud.

Right now I am still running stock headers and cats. Maybe after this weekend I'll get a chance to install my Borlas.
hink01wag
06-19-2009, 05:39 PM
i took mine completely out... i installed the ebay header and strait pipe back to a turbo muffler. f'n loud so i had a glass pack laying around kind of quieted it down, still loud as hell. if you want to get rid of your cats get a o2 spacer for the rear o2 and you'll never have a cel again for the cats. i had to make a spacer w/ a 90 in it to miss the heat shield.