CAT question

99SilverCX · Post by **99SilverCX** » Thu Feb 26, 2009 1:24 am

Car: 99 EM1
I'm just trying to plan my exhaust work on the SI, the thermal research exhaust is getting annoying and I want to get my Highend tri-y installed in the SI.
Header: Highend tri-y with 2.5' collector (has primary O2 bung).
Exhaust: Apexi WS2 2,5'
Since the stock SI cat is 2.25' (I think), I'd like to get an aftermarket CAT that's 2.5' for more flow, but my question is, does it have to have the O2 bung in the middle like the stock SI CAT? or can I mount the secondary O2 behind the cat to keep the emissions happy?

Midori · Post by **Midori** » Thu Feb 26, 2009 1:33 am

you wont be able to use a cat with the tri Y without modifying the exhaust, its made to delete the cat

edit: unless its made for an SI? but most tri Y's are universal B series headers...

99SilverCX · Post by **99SilverCX** » Thu Feb 26, 2009 3:04 am

MidoriMiller;167290 wrote:you wont be able to use a cat with the tri Y without modifying the exhaust, its made to delete the cat

edit: unless its made for an SI? but most tri Y's are universal B series headers...

yeah, I know about that, I had this header on my silver hatch and the cat was just like a foot farther back. They don't make WS2 for a 96-00 hatch with B-series, so the exhaust had to be modified from the get-go on that car.

Midori · Post by **Midori** » Thu Feb 26, 2009 4:01 am

i see.. i say just use the stock cat, or buy an adjustable test pipe because world sport 2 is wayyyy quiet anyway

99SilverCX · Post by **99SilverCX** » Thu Mar 05, 2009 3:58 am

MidoriMiller;167337 wrote:i see.. i say just use the stock cat, or buy an adjustable test pipe because world sport 2 is wayyyy quiet anyway

Don't really want to use the stock cat because that is too much of a bottleneck, and don't want to use a test pipe cuz it needs to be emisison legal...

tcr03 · Post by **tcr03** » Thu Mar 05, 2009 4:30 am

What you gain in performance by removing the cat does not out weight the awfull smell and greenhouse gas you will be spilling into the air. Just leave the stock one on. Unless your pushing high horsepower with a turbo you wont gain much by changing it

N2HIFI · Post by **N2HIFI** » Thu Mar 05, 2009 5:05 am

99SilverCX;169058 wrote:Don't really want to use the stock cat because that is too much of a bottleneck, and don't want to use a test pipe cuz it needs to be emisison legal...

i dont really think that 1/4" of step down will really be that noticeable on your stock b16.

you could by a ITR 2.5" cat but they are about 200 even for a aftermarket one from like magnaflow

RyanA · Post by **RyanA** » Thu Mar 05, 2009 11:59 am

Just get a REAL aftermarket cat (not high flow POS that is resonator) that is the stubby one. Get one that is 2.5" ID. The shorter cat fits pretty well. Have your cat back on the car and the header on there. Put your flange for the header on and a flange for the cat back and put the stubby cat in the middle. Add little pieces of pipe, if needed, and weld up. If you don't use a flex joint, you need to make sure you use spring bolts so the exhaust has somewhere to move. You can put the rear O2 behind the cat or in the back of it. Either way will let it make the ECU happy.

HardCore97 · Post by **HardCore97** » Thu Mar 05, 2009 3:10 pm

heres a magnaflow cat for 65 bucks CLICK but you will have to run an o2 sensor behind it since it doesnt have on 02 bung

forcefed · Post by **forcefed** » Thu Mar 05, 2009 4:16 pm

wow i didnt know they were so cheap,heck u can sale a used one for 80 bucks around here