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Discussion Starter · #1 · (Edited)
I know its kinda taboo around here but i have a couple questions.

does the O2 sensor HAVE to be in the cat? I want to buy a 200 or 100 cpsi cat and weld it in myself then just weld in the o2 sensor right after it.

lastly, is there anything bad about removing the cat all together? I would put in a straight pipe with the
o2 sensor. I mean like will I get bad fumes in my cab as some people say? or will it be bad ont the turbo?

I have the stock exhaust with a magnaflow muffler. I dont have emissions testing and never will.


thanks
 

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Rear O2 needs to be post cat and yes the primary needs to be pre-cat. The pre-cat can be direct into the downpipe whereas with a aftermarket cat u will generally require a spacer to remove it from the direct exhaust stream to reduce risk of a cat deficiency fault.

I wouldn't recommend straight pipe. U won't see any performance difference between high flow cat and without and will just make raw hydrocarbons puke out the tail pipe.
 

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you can buy my high flow 3" cat i have for sale... its brand new and super cheap! just pm
 

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Discussion Starter · #4 ·
you can buy my high flow 3" cat i have for sale... its brand new and super cheap! just pm
I would but i believe my stock exhaust is only 2.5 in
 

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Discussion Starter · #5 ·
Rear O2 needs to be post cat and yes the primary needs to be pre-cat. The pre-cat can be direct into the downpipe whereas with a aftermarket cat u will generally require a spacer to remove it from the direct exhaust stream to reduce risk of a cat deficiency fault.

which sensor needs the spacer? the post cat o2? I assume the pre cat shou;d not be messed with, so ill just leave it where it is.
 

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Yeah rear O2 will likely need spaced. Some cats seems to be more efficient than others.
 

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Discussion Starter · #7 ·
ya im trying to get an effiecient one to see if i can get away with no spacer. metal core made in the usa seems like a good bet to me. and at 120 bux for 200 cpsi you cant go wrong.
 

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I would but i believe my stock exhaust is only 2.5 in
Stock piping is 60mm outside diameter. ID is more like 2.25".
 

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I don't know Colorado's laws, but make sure there isn't a visual inspection like in Virginia. Part of the emissions testing here is a visual inspection of the exhaust system for the presence of a catalytic converter, and the absence of any type of spacers (ask me how I know....). If you have a spacer you'll fail on the spot. I hope Colorado is more like Florida, where they don't even test period!!
 

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If your worried about a spacer being spotted, mount the o2 snesor where it can't be seen. I've had cars where they are mounted on top of the pipe (I have no idea what spacial limitations we have on the P2 chassis)

I dont have emissions testing and never will.
:mad:
 

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I've used the Jetted "J" Spacer made by RAI Motorsports with great success. It keeps the CEL off with my GTI running a 3'' catless downpipe. It comes with 3 different jets that you can swap in and out in a few minutes so you can basically fine tune the amount of flow reaching the sensor.
 

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Discussion Starter · #12 ·
Stock piping is 60mm outside diameter. ID is more like 2.25".
I can use my flare press to get the exact fitment on a 2.5 in pipe.
 

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Discussion Starter · #13 ·
I don't know Colorado's laws, but make sure there isn't a visual inspection like in Virginia. Part of the emissions testing here is a visual inspection of the exhaust system for the presence of a catalytic converter, and the absence of any type of spacers (ask me how I know....). If you have a spacer you'll fail on the spot. I hope Colorado is more like Florida, where they don't even test period!!
nope, in my county they dont even test period. If I was in denver, boulder, or fort collins things would be alot different.
 

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Spacer or tune will solve cel issue
 
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