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      01-16-2014, 08:07 PM   #1
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Question N54 335i Secondary Catalytic Converter Options

I will be putting in cat-less DPs, and after looking over the aftermarket exhausts and seeing how the stock exhaust is an all-welded, one-piece system from the DPs back, what have others done in regards to putting in some sort of catalytic converter system in place?

I definitely do not want to run completely cat-less here in Cali, but more importantly to avoid the obnoxious "smell" of a cat-less system that many have complained about.

It seems like the options are:

1) Completely custom "cat-back" exhaust by cutting after the cats and putting in your favorite flavor of muffler.

2) Modifying an aftermarket exhaust to install after the stock cats.

3) Modifying an aftermarket exhaust to install aftermarket "high flow" catalytic converters.

4) Using an aftermarket exhaust already designed to be installed "cat-back" (I'm not aware of any for the N54 335i Sedan).

My choice of exhaust are an Always Evolving formerly Autobahn Exotics (which I was told is being discontinued), an HKS (seems to be the next best in performance potential), and Active Autowerke. I chose the first two because of performance AND mellow-yet-sportive sound, while the AA has the same sound quality I prefer, I haven't seen any dyno comparisons over stock.

Opinions and experiences?
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      01-16-2014, 09:56 PM   #2
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I was in pretty much the same boat as you. Was looking at HKS or AE exhaust systems, but none of them offer cats as an option. AE said they would check with their fabricator, but I never heard back. They might be closed already. That whole situation is just sad. Paul was a customer of ours, and I would see him around town every now and then.

Anyway, the thought of cutting up a brand new exhaust system like that made me reconsider. I'm very happy with what I ended up doing, and likely wouldn't change a thing if I were to do it again. My setup is:

AR catless downpipes
stock secondary cats
stock midpipe w/ stock E90 resonator
335is mufflers (with tips shortened for proper look on E90)

For me, the tone and sound level are perfect. Smell is basically non-existent. There is no rasp, which I'm guessing the stock E90 resonator is responsible for eliminating. The black tips look cool, too, without looking too gaudy. I have a couple videos of the sound. I'll try to post one for you.
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      01-16-2014, 11:47 PM   #3
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If you can post the sound clip, yes please.

Regarding AE, when you mentioned "Paul" and "just sad" I had no idea what you were talking about but I had a hunch, so I Googled and discovered that AE was actually run by Paul Walker and Roger Rodas. Just… wow.
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      01-17-2014, 12:30 AM   #4
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AE Exhaust ftw! Here's my review on it with videos..

http://www.e90post.com/forums/showthread.php?t=907580
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      01-17-2014, 09:26 AM   #5
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I believe the newly released Cobb catback exhaust has cats.
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      01-17-2014, 10:45 AM   #6
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Quote:
Originally Posted by ihc95 View Post
I believe the newly released Cobb catback exhaust has cats.
Hmm...

Well, even though their description of their new exhaust mentions "cat-back,", the photos indicate that it's just like all other aftermarket exhausts and replaces the entire stock exhaust from the downpipes back:



The little canister on the "test pipe" section is a "Helmholtz Chamber' for reducing resonance:



So I'm not sure what this inline chamber is on the mid-pipe:



From its size, it looks to be a resonator, but it could also be a high flow catalytic converter. If it's the former, then their interpretation of "cat-back" is that their system is after the primary cats located in the factory DPs, while the latter could allow them to technically label it as a "cat-back" exhaust which really replaces the OEM cats with a single aftermarket cat.

I'd like to really like to hear some sound clips. And I also wonder about it's performance potential seeing how it's basically a single exhaust system.
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      01-17-2014, 10:48 AM   #7
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The Cobb has a resonator, no cats.
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      01-17-2014, 12:16 PM   #8
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My mistake guys. Thanks for correcting me.
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      01-17-2014, 01:28 PM   #9
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What about an axel back like billy boat?


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      01-17-2014, 01:58 PM   #10
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Hmm, interesting. From the one sound clip on Bavarian Auto, sound quality is along my preferences: not "rattley" at idle nor too loud. But another sound clip on YouTube sounded almost silent with no appreciable change in tonal quality. I couldn't find any other sound clips of their "axle back" (non-Sport) system.

And $1,300 plus change seems a little too pricey for essentially a pair of mufflers and tips that you have to cut into and installed onto the stock exhaust requiring the services of an exhaust shop (thus adding to the price), though it does have a OEM-style flapper valve built in on the left tip.

Still worth considering and on my list, similar to the 335is mufflers, though the latter may also be a rather expensive proposition if purchased brand new since waiting around to find a low-cost used set locally may be a frustratingly long and potentially fruitless wait.
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      01-17-2014, 03:21 PM   #11
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As for adding cats, how about something like this:
http://www.mandrelbendingsolutions.c...CPSI%29/Detail

Or one of these (super pricey):
http://www.hjsna.com/categories/Tuni...-200-C.P.S.I./
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      01-17-2014, 08:39 PM   #12
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Sorry, it's not the best sound quality on the driving video. I had my GP in the sealed case, which is really meant for high speed runs. I need to try to take another one that catches the sound better. The last video gives a pretty decent representation of how it actually sounds during different driving situations.

And yeah, AE was owned by Paul Walker and Roger Rodas. Paul had a house just a few miles from where I live in Santa Barbara.





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      01-17-2014, 09:13 PM   #13
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Quote:
Originally Posted by Augster View Post
I will be putting in cat-less DPs, and after looking over the aftermarket exhausts and seeing how the stock exhaust is an all-welded, one-piece system from the DPs back, what have others done in regards to putting in some sort of catalytic converter system in place?

1) Completely custom "cat-back" exhaust by cutting after the cats and putting in your favorite flavor of muffler.

2) Modifying an aftermarket exhaust to install after the stock cats.

3) Modifying an aftermarket exhaust to install aftermarket "high flow" catalytic converters.

4) Using an aftermarket exhaust already designed to be installed "cat-back" (I'm not aware of any for the N54 335i Sedan).

My choice of exhaust are an Always Evolving formerly Autobahn Exotics (which I was told is being discontinued), an HKS (seems to be the next best in performance potential), and Active Autowerke. I chose the first two because of performance AND mellow-yet-sportive sound, while the AA has the same sound quality I prefer, I haven't seen any dyno comparisons over stock.

Opinions and experiences?
You have a sedan, which already has smaller secondary cats so the smell won't be overpowering. Regarding sound, you'd probably be best off with a rear section exhaust (Akra, Billy Boat, UUC/Corsa, Eisenmann, etc), otherwise you're buying a full catback which you're gonna have to hack up to put custom cats in.

Performance wise, you'll be lucky to net 10 WHP. On stock turbos you're just not moving enough air that the OEM exhaust is restrictive. All the power in the exhaust system is in going to catless DPs.
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      01-17-2014, 09:35 PM   #14
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PE ftw! Made for this car. No drone. Burble and crackle. East install. Sounds better with age (dine wine?).

Recorded with Sony Action Can with extended external Audio Technics lavalier mic run through the rear pass-thru and out the trunk....clipped to the license plate. First video with mic setup and I think it turned out swell.

Will be going to my favorite twisty back roads this weekend to catch some more vid and try to emulate the sound of tracking the car.


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      01-17-2014, 09:40 PM   #15
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Quote:
Originally Posted by Mit_Boost View Post
You have a sedan, which already has smaller secondary cats so the smell won't be overpowering. Regarding sound, you'd probably be best off with a rear section exhaust (Akra, Billy Boat, UUC/Corsa, Eisenmann, etc), otherwise you're buying a full catback which you're gonna have to hack up to put custom cats in.

Performance wise, you'll be lucky to net 10 WHP. On stock turbos you're just not moving enough air that the OEM exhaust is restrictive. All the power in the exhaust system is in going to catless DPs.
Yeah, a full downpipe-back exhaust really isn't worth the investment for the power gained or the downsides for daily driving (smell, resonance/drone). I did the 335is mufflers for the sound, and OEM fit/finish is what I was looking for. There are plenty of aftermarket axle-back systems depending on what look and sound you're after.

But for what it's worth, ALL N54 3-series models have secondary cats from the factory. The sedans just have an extra resonator/muffler (instead of an X-pipe) that's located towards the rear of the midpipe.
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      01-18-2014, 12:20 AM   #16
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Quote:
Originally Posted by Mit_Boost View Post
You have a sedan, which already has smaller secondary cats so the smell won't be overpowering. Regarding sound, you'd probably be best off with a rear section exhaust (Akra, Billy Boat, UUC/Corsa, Eisenmann, etc), otherwise you're buying a full catback which you're gonna have to hack up to put custom cats in.

Performance wise, you'll be lucky to net 10 WHP. On stock turbos you're just not moving enough air that the OEM exhaust is restrictive. All the power in the exhaust system is in going to catless DPs.
I will be installing Vargas Stage 2 turbos by summer, so the performance abilities of exhaust system after the catless DP's should be more pronounced: how much performance is the question. Regardless, I must have cats in place somewhere along the line.

If the performance potential with a full aftermarket exhaust like AE with custom added cats is pronounced over an axle-back like Billy Boat for a VTTS2/Catless DP/IC/Cobb/E85 setup, then I would lean to cutting up a full exhaust, especially if the price point for an axle-back is in the $1,400 range. But if I can score a low-cost 335is exhaust, used or otherwise, I'm looking at that option presently.

Quote:
Originally Posted by FCobra94 View Post
As for adding cats, how about something like this:
http://www.mandrelbendingsolutions.c...CPSI%29/Detail

Or one of these (super pricey):
http://www.hjsna.com/categories/Tuni...-200-C.P.S.I./
Certainly aftermarket cats is something I'm looking at if I go with a full-exhaust system like AE, but nothing so astronomically expensive as those HJSNA's!
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      01-18-2014, 12:25 AM   #17
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Quote:
Originally Posted by BMWM.D. View Post
The last video gives a pretty decent representation of how it actually sounds during different driving situations.

Yes, I like the sound of this, and it's more representative of what I will be running with AR carless! And I don't really need "bling bling" massive tips; "sleeper" is what I'm shooting for.

I just can't nail down the part numbers of the 335is mufflers, just in case I have to order new ones because no used ones were to be found locally.
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      01-18-2014, 03:22 AM   #18
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BMW PE, or 335is OE muffler if you want more mellow.
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      01-18-2014, 09:29 AM   #19
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BMW PE, or 335is OE muffler if you want more mellow.
Although I prefer mellow-sportive, not at $1,700+shipping for BMW's PE for basically just a sound upgrade. At that price-point, I'd rather pop for an AE hands down to also enjoy the performance potential with my upgrades planned.
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      01-18-2014, 10:30 AM   #20
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Quote:
Originally Posted by Augster View Post
Yes, I like the sound of this, and it's more representative of what I will be running with AR carless! And I don't really need "bling bling" massive tips; "sleeper" is what I'm shooting for.

I just can't nail down the part numbers of the 335is mufflers, just in case I have to order new ones because no used ones were to be found locally.
I'm a fan of the sleeper thing too. The "is" mufflers are part numbers: 18307604830 and 1830760483. ECS Tuning sells them for about $820 new for the set, but you might be able to find them cheaper. Every once in a while used one pop up for sale, just got to keep your eyes open.

I had mine welded in for a factory look. And since they are for the coupe and convertible models, the tips stick out an extra inch or so unless you have them shortened. Still a much better deal than the BMW PE systems., and you still have the vacuum flap on the left muffler if you want to quiet the car down for certain occasions.
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      01-18-2014, 12:38 PM   #21
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Quote:
Originally Posted by Augster View Post
I will be installing Vargas Stage 2 turbos by summer, so the performance abilities of exhaust system after the catless DP's should be more pronounced: how much performance is the question. Regardless, I must have cats in place somewhere along the line.

If the performance potential with a full aftermarket exhaust like AE with custom added cats is pronounced over an axle-back like Billy Boat for a VTTS2/Catless DP/IC/Cobb/E85 setup, then I would lean to cutting up a full exhaust, especially if the price point for an axle-back is in the $1,400 range. But if I can score a low-cost 335is exhaust, used or otherwise, I'm looking at that option presently.
Even at that point, you'll see marginal gains. Honestly I'd recommend keeping your OEM rear section and getting SuperSprint midpipes/a custom mid section with sport cats of your choice.

The fact that your dead set on having cats is going to create a greater restriction in the exhaust then going from the OEM diameter piping (~2.5") to a true 3" exhaust on the HKS, AE, COBB full exhaust. I don't think anyone has proven that an exhaust has yielded more than 10-15 WHP, and those higher gains are on the Single Turbo setups pushing well over 600 WHP.
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      01-18-2014, 01:09 PM   #22
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Quote:
Originally Posted by Augster View Post
Although I prefer mellow-sportive, not at $1,700+shipping for BMW's PE for basically just a sound upgrade. At that price-point, I'd rather pop for an AE hands down to also enjoy the performance potential with my upgrades planned.
Got my PE for $1200 shipped. Just gotta poke around... $1700 is crazy.
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