[Augster]

Originally Posted by Mit_Boost

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.

I'm not sure how 2.36 vs 3" got into this, but I put the HKS and AE full-exhaust aftermarket systems on my list because of all the positive reviews, recommendations, sound quality, and even a test comparison by pseudo-professional "journalists" (e.g. Grassroots Motorsports Executive Decisions article). I actually never checked on the pipe diameter used in any of these setups, so if it's 2.5 vs 3", or even the stock 60mm/2.36", I'm not too concerned so long as performance doesn't suffer in any way (performance increase is preferred, of course) with the mods I will be adding.

But it's not just about performance: for me, the sound quality is equally, if not more important, which is why I emphasized "performance AND mellow-yet-sportive sound" in my original post. Sure, I can do what you recommend by sticking with the stock 335i mufflers and simply switching to High Flow Catalytic converters but I already know I don't like the sound of catless DPs on an otherwise stock 335i exhaust; otherwise I wouldn't be posting my question, which is really about solutions for catalytic converters on aftermarket exhausts (I definitely did NOT want to pose a "which is the best exhaust" ad nauseum thread). I certainly don't want loud and obnoxious either. So it's a compromise and balance.

One thing not mentioned is the weight savings by going to a full aftermarket exhaust and would be a nice benefit to aim for.

The ultimate arbiter in all this for me will be price points, because if a pair of mufflers will cost me $1.5k, that's in the ballpark of full-on exhaust systems and would sway me to the latter.

Though, taking a cue from your suggestion of using HFC's, I think if I couple that with a pair of 335is mufflers, worst case scenario of having to buy them brand new for ~$700 for a set, that might be a viable option. Did I say I like them sounds of the 335is muffs?

Originally Posted by stashtrey

Got my PE for $1200 shipped. Just gotta poke around... $1700 is crazy.

After some digging, best I can find is $1,500 plus shipping. Would like to know where you got yours for $1,200. But the majority (not everyone) agrees the 335is exhaust sounds "better" so I think my worst-case solution mentioned above of sticking with a BMW exhaust by switching to 335is mufflers plus high-flow cats would still keep me below even a $1,200 price point; perhaps sub-$1,000 if I do all the work myself (have my own MIG welder or can resort to exhaust band clamps for the quick-n-dirty).

[Augster]

One thing I failed to mention: I need to switch back to an all stock exhaust every two years to pass the Smog man here in Cali. Which means if I modify the stock secondary cats in any way instead of going full aftermarket, I have to make it reversible.

I'm already prepared to switch out DPs back and forth and will be keeping my stock DPs in storage, along with my stock exhaust in whatever form I ultimately decide upon for my "everyday" exhaust.

[BMWM.D.]

Originally Posted by Augster

One thing I failed to mention: I need to switch back to an all stock exhaust every two years to pass the Smog man here in Cali. Which means if I modify the stock secondary cats in any way instead of going full aftermarket, I have to make it reversible.

I'm already prepared to switch out DPs back and forth and will be keeping my stock DPs in storage, along with my stock exhaust in whatever form I ultimately decide upon for my "everyday" exhaust.

That's another reason I chose to do what I did. Besides the 335is mufflers, my exhaust system is stock. All I need to so to be totally smog compliant is swap my stock downpipes back in.

[Deluvio2527]

Originally Posted by stashtrey

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.

what is ur exhaust set up sir?

[BM3Rrrr]

Originally Posted by Deluvio2527

what is ur exhaust set up sir?

Thread was from 6 years ago....poster you commented on hasn't been online in 1 1/2 years

[iqraceworks]

Originally Posted by Augster

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?

Honestly, unless you are sticking your head right at the exhaust tip and sucking in a huge breath of exhaust.......I haven't really noticed any "obnoxious smell" after I did my catless DPs. Not sure I would try to install an extra set of convertors just because of fear of a smell......

[Emilime75]

Pretty sure this thread is talking about the secondaries.

Originally Posted by iqraceworks

Honestly, unless you are sticking your head right at the exhaust tip and sucking in a huge breath of exhaust.......I haven't really noticed any "obnoxious smell" after I did my catless DPs.

You should get your nose checked. There's definitely a stench...even when running a healthy dose of E85. On straight pump, it's 2x worse.

[iqraceworks]

Originally Posted by FCobra94

You should get your nose checked. There's definitely a stench...even when running a healthy dose of E85. On straight pump, it's 2x worse.

I sure haven't noticed anything......but I'm not constantly sniffing my exhaust either. It's exhaust.....it's not supposed to smell "good"

Originally Posted by iqraceworks

It's exhaust.....it's not supposed to smell "good"

Well neither do toilets, but something tells me that if you removed the door off a bathroom most people would notice that more too.

[iqraceworks]

Originally Posted by FCobra94

Well neither do toilets, but something tells me that if you removed the door off a bathroom most people would notice that more too.

Congratulations...you won the internet today

Worrying about how your exhaust smells makes about as much sense as worrying about what your brake pads smell like when they get hot.

It would appear that you enjoy huffing hydrocarbons by the tank full...and it shows.

[iqraceworks]

Originally Posted by FCobra94

It would appear that you enjoy huffing hydrocarbons by the tank full...and it shows.

Ok