[AndyR83]

I've been doing lots of research and reading lots of threads regarding exhaust mods, but I'm still having a hard time figuring out the real deal when it comes to secondary cats.

For starters, I can't tell if my car even has them. I've read in some places that only the xi has them, in other places it appears all 335's do. I can't get my head under there to actually look for myself, so I'm left wondering if I have them or not.

From what I've read, leaving the secondary cats in place helps reduce exhaust fume odor when swapping to catless downpipes, which I am doing this week. To that extent, I'd like to find out if I have them (hoping I do) and make sure they are left intact.

This gets even more confusing for me when the "cat back exhaust" is discussed. What does this mean? When you add a cat back is it behind the secondary cats? If I have catless dp's and I want to add a catback later on down the line do I need to tell somebody that I have doing the install to leave the secondary cats there? Is this a non-issue because I don't have them to begin with?

sorry for sounding like a clueless noob but... well... I'm a clueless noob. I've read and searched a lot, still haven't figured it out.

Thanks!

[E90Company]

Everything you stated is right, but:

Catback exhaust is from the downpipe, back. (includes secondary cats)

The E9X N54's all have secondary cats.
N55 XDrive has secondary cats, the RWD N55 does not.

[benzy89]

Secondary cats are in all 335s, the only real difference between the coupe & sedan exhaust system is the H/X-pipe in the coupes (can't remember which)

Cat Back Exhaust is basically from the DP (the primary cat) to the mufflers. Catback Exhaust replace all the piping that connects to the DP back, while Axle-Back Exhaust only replace the muffler section (from the rear Axle back). If you're concerned about drone/exhaust smells, just get an Axle-Back Exhaust & leave the OEM midpipes/secondary cats in tact.

The 335 exhaust is fairly free flowing (an exhaust upgrade really doesn't offer significant performance gains to begin with), so all you're really doing is to change your exhaust note, there are plenty of quality Axle-Back Exhaust options to go with (UUC/Corsa, BMW PE, Eisenmann, Billy Boat, etc) that will give you a quality sound change, without significant drone/rasp or smelly catless exhaust


Side Note: Andy, where are you from in PA. Anywhere close to KOP (King of Prussia)?

[AndyR83]

Thank you both for your helpful and informative posts! You have clarified things for me perfectly.

Benzy, I live in the Scranton/Wilkes-Barre area of northeast PA, about 45m from NY or NJ.

[spool twice]

IHMO the car sounds better with secondary cats removed vs. primary cats.