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      11-26-2012, 09:01 PM   #17
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Drives: 2008 128i
Join Date: Mar 2011
Location: South Jersey

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2008 BMW 128i  [5.00]
Originally Posted by Greenkirby21
sorry to bump an old thread guys but I wanted to hear everyones opinion on this since I don't know.

My car, an N52, has the lower picture from above, meaning I have both primary and secondary cats. I live in Texas, which I'm not even sure is a carb compliant state or not.

Anyways, I was wondering what happens if the secondary or primary cats are removed(pick one, not both).

I read online that removing the first set would yield the biggest gains as they are the most restrictive, but would it cause a CEL to occur or something of that sort? Would I fail the emissions test?

I read that removing the second set would yield little to no gain in power and just slightly increase the noise your car makes, and it also wouldn't produce any CEL or anything. Therefore, its not "worth it" to remove them, unless you want more sound.

I was just curious because I was searching through the forums and found this. I always wondered why my car has two sets of CATS, and if removing one would be beneficial or not.

Edit: Funny that my car has two cats and is considered ULEV-II.. it smells of gasoline when I turn on the car initially >_>
I thought that the magna flow exhaust deleted the secondary cats on the 128 since it connects to the bottom of the exhaust manifold. Assuming you still have the mf cat back exhaust. If you did delete the primary cats you would get a cel.
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