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      01-05-2013, 05:21 PM   #18

Drives: Current:135i Sold:335i sedan
Join Date: Mar 2007
Location: City of Angels

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Originally Posted by Tee-Dub View Post
I keep reading how restrictive the 135's stock exhaust is though. I wonder if they are referring to the catted mid-pipe on earlier years (mine) or is it the axle back that is so restrictive? For those of you that installed cat-less downpipes but kept the stock section, did you have any issues with the secondary cats getting clogged up?

Primary and Secondary cats are identical. Why would the secondary get clogged up and from what?

On both 335 and 135, the restriction on the exhaust are the Cats, the axel back aka muffler section is no issue.

Removing primary cats provides most hp gains (across the board), and removing secondary cats gives 10whp (Mainly top end).

Removing the muffler/axel back provides no real gains except for sound and perception that the car is faster.