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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > How restrictive is the 335i Muffler?



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      03-22-2007, 01:46 PM   #1
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How restrictive is the 335i Muffler?

When I had my car up on a rack the other day having an allignment I was taking a close look at the Boysen silencer on our cars and it actually looks to be pretty high quality with nice welds, and a pretty cool design with the 2 seperate sections and a cross pipe linking the 2 muffler bodies. It looks much better than the OEM e46 M3 muffler actually.

I am sure this Boysen muffler is heavy as hell but I wonder how well it flows compared to an AM setup. It is pretty tempting to just remove the secondary cats, resonator and the crimped, acute angle bends in the oem mid-section and leave this muffler since I am guessing that will have awesome sound like a more aggressive and a little louder version of OEM.
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      03-22-2007, 01:51 PM   #2
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Were you able to get a picture while you had it up? I'd love to see what the bottom looks like.

Thanks,
T
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      03-22-2007, 01:55 PM   #3
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That actually sounds like an idea. Do it! I may try it my self unless someone here with real knowledge in exhaust systems
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      03-22-2007, 02:24 PM   #4
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Stock exhaust is pretty restrictive.... there are so many curshed bends in the system, regardless of how good the welds are on it, and not to mention the mid muffler and other set of cats on it.. It sounds nice but still restrictive... anytime you have a better flowing exhaust sytem on a turbo car, you will make more power and a lot more tq as well.
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      03-22-2007, 03:43 PM   #5
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Originally Posted by CEA 3 View Post
Stock exhaust is pretty restrictive.... there are so many curshed bends in the system, regardless of how good the welds are on it, and not to mention the mid muffler and other set of cats on it.. It sounds nice but still restrictive... anytime you have a better flowing exhaust sytem on a turbo car, you will make more power and a lot more tq as well.
Thanks bro, I think you misunderstood what I was saying. I definitely plan on losing the secondary cats, the resonator, the crimps and bends, etc. I'm just talking about the idea of keeping the muffler itself.

By the way, I am still interested in the muffler shop you were talking about in torrence. Maybe I could get them to do the job for me. If it doesn't turn out as hoped I could just remove the oem and add a couple of Magnaflows. Did you ever get the address by any chance?

Thanks
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      03-22-2007, 03:45 PM   #6
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Quote:
Originally Posted by Terry Burger View Post
Were you able to get a picture while you had it up? I'd love to see what the bottom looks like.

Thanks,
T

Sorry Terry, I didn't take any pics. I only had my Razr but didn't even think of taking pics. Once I have time I am going to muffler shop and I'll take some pics then. I am hoping CEA can send me the address of his guys because he said they do good work at good rates.
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      03-22-2007, 03:48 PM   #7
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Yeah its hard to find a guy that won't "freak out" about removing the rear cats. If you guys know anyone local let me know.
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      03-22-2007, 05:25 PM   #8
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Quote:
Originally Posted by radgator1 View Post
I am sure this Boysen muffler is heavy as hell
Has anyone that has replaced their stock exhaust weighed the thing? I'm guessing there's a fair amount of weight savings to be had, in addition to any performance gains, but would love to have some numbers.

While I'm at it, does anyone know if removing the secondary cats is legal in California?

Thanks,
Richard
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      03-22-2007, 05:41 PM   #9
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Originally Posted by rsjames View Post
Has anyone that has replaced their stock exhaust weighed the thing? I'm guessing there's a fair amount of weight savings to be had, in addition to any performance gains, but would love to have some numbers.

While I'm at it, does anyone know if removing the secondary cats is legal in California?

Thanks,
Richard
No exhaust mods are legal for street use in California. If you are worried about strictly following the law then don't mod your car at all since that is the only way to stay 100% legal.
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      03-22-2007, 06:13 PM   #10
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you are legally allowed to change the catback portion, if your db level doesn't exceed a certain number.

can't touch the cat, or the downpipe.

i think by removing the cats on the oem exhaust system alone would give you significant gains...less back pressure is always a plus for turbocharged cars.

other than your car stinking like crap, some people wrap cat shields around test pipes and stuff the inside with muffler repacks to pass baton tests from cops. this will make the test pipe pass visual test too since it looks like a cat from the outside.

once you're sent to the ref station though u'd have to swap the oem cat back on, not sure how easy that is to do with the 335i's oem exhaust design. for my Evo it's 4 bolts.
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      03-22-2007, 06:26 PM   #11
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Quote:
Originally Posted by rsjames View Post
While I'm at it, does anyone know if removing the secondary cats is legal in California?

Thanks,
Richard
Technically, removing any cats that come from the factory on your car, without documented evidence that they have lost their efficiency, become restricted or are otherwise in need of replacement is in violation of federal law, not just California. And then you are required to replace them with new cats, though you can use aftermarket units.

This law can be a difficult one to enforce... ultimately, it's your risk.
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      03-22-2007, 07:25 PM   #12
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Quote:
Originally Posted by fusionchicken View Post
you are legally allowed to change the catback portion, if your db level doesn't exceed a certain number.

can't touch the cat, or the downpipe.

i think by removing the cats on the oem exhaust system alone would give you significant gains...less back pressure is always a plus for turbocharged cars.

other than your car stinking like crap, some people wrap cat shields around test pipes and stuff the inside with muffler repacks to pass baton tests from cops. this will make the test pipe pass visual test too since it looks like a cat from the outside.

once you're sent to the ref station though u'd have to swap the oem cat back on, not sure how easy that is to do with the 335i's oem exhaust design. for my Evo it's 4 bolts.
The 335i has 2 sets of cats and we are only talking about removing the secondary cats so there is no need to go through all that hassel. The car still sniffs clean with only the primary cats. the only one who would know you removed them is BMW and I dont think they would particularly care unless you were trying to make a warranty claim on part of the exhaust system.
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      03-22-2007, 09:27 PM   #13
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It's been a long time since I've been in CA...but new cars don't require any emissions testing/inspection for the first four years of their life (though I guess that can vary from state to state). So...you can do whatever and have four years to think about how to go back to stock.

If this ISN'T the case for CA, then obviously disregard.
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      03-23-2007, 02:23 PM   #14
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Quote:
Originally Posted by andrew20195 View Post
Technically, removing any cats that come from the factory on your car, without documented evidence that they have lost their efficiency, become restricted or are otherwise in need of replacement is in violation of federal law, not just California. And then you are required to replace them with new cats, though you can use aftermarket units.

This law can be a difficult one to enforce... ultimately, it's your risk.
Thanks. I guess the question is really whether the Feds or the state of California view these secondary cats as catalytic converters, or something else. I'm waiting on my car, and haven't been under a 335, so I'm kind of flying blind here. Anybody know what these things actually do?

However, Railgun is right - the state of California doesn't do emissions tests on new cars - only after a car is four years old. I also suspect, unless it looks homemade, that your typical smog station attendant wouldn't be able to pick out an aftermarket exhaust unless it was really loud (which I don't want - just enough so that I can actually hear the thing).

But, back to my original question - anybody know what the cat-back portion of the exhaust weighs?

Richard
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      03-23-2007, 02:38 PM   #15
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Quote:
Originally Posted by rsjames View Post
Thanks. I guess the question is really whether the Feds or the state of California view these secondary cats as catalytic converters, or something else. I'm waiting on my car, and haven't been under a 335, so I'm kind of flying blind here. Anybody know what these things actually do?

However, Railgun is right - the state of California doesn't do emissions tests on new cars - only after a car is four years old. I also suspect, unless it looks homemade, that your typical smog station attendant wouldn't be able to pick out an aftermarket exhaust unless it was really loud (which I don't want - just enough so that I can actually hear the thing).

But, back to my original question - anybody know what the cat-back portion of the exhaust weighs?

Richard
Richard,

http://www.e90post.com/forums/showthread.php?t=44798

According to UR, the factory is 78lbs and theirs is 55lbs. Also, the 330i muffler is about 30 lbs if that helps any.

Good luck!
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      03-25-2007, 12:41 AM   #16
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Quote:
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Yeah its hard to find a guy that won't "freak out" about removing the rear cats. If you guys know anyone local let me know.
I'm new to this forum, but WILL be able to help.
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      03-25-2007, 12:48 AM   #17
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I'm new to this forum, but WILL be able to help.
Do you do muffler work?
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      03-25-2007, 12:54 AM   #18
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Quote:
Originally Posted by 335hopefull View Post
I'm new to this forum, but WILL be able to help.
I think both of us should be able to help this forum.

Once the car has broken in somewhat (only 260 miles on it, and Ive had it for 24 hours...lots of driving!), I will be fabbing up a prototype system for the sedan, perhaps the coupe if someone is willing to donate their car for a day or two.

It won't look as good and shiny as the major brand ones out there, but considering my old boss and I have some pretty damned good welding skills (well he TIGs too, so he has me beat), I figure some good 321 stainless to borla mufflers should do the trick. HP gains will be there, maybe not as much as the big guys out there, but for the price and the quality of pipe and mufflers, if I can achieve a good tone (if I could replicate the M3 GTR sound I would be in heaven) and make some good power gains while keeping the price below the 4 digit range, I think we'd have a seller no?
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      03-25-2007, 12:58 AM   #19
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Do you do muffler work?
Yes in the La Puente West Covina area. Thats Los Angeles County.
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      03-25-2007, 01:26 AM   #20
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Yes in the La Puente West Covina area. Thats Los Angeles County.
You have PM. You're right in my area
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