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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 > CARB legal modded Exhaust



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      09-10-2018, 09:50 PM   #1
Twinning_N54
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CARB legal modded Exhaust

So I finally starting my exhaust build for my 09 335XI, being a AWD my exhaust options have always felt limited to $1k+

I have decided to put together my own kit with 2.5" magnaflow mufflers and high flow cats for both main and secondary cats since I do live in California and have to abide by the California Air Resources Board rules.

I'm planning to get cat-less downpipes and installing Cali legal HFC right after the DP and adding the 2nd cats right before the rear axle (crazy bends)

so therein lays my question. Has anyone tried this setup? I'm thinking its going to be the best of both worlds... my concern is the length/position of the sensors.

any and all input is welcomed

thanks!
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      09-11-2018, 09:42 AM   #2
ferocity02
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Your plan is far from CARB legal. You are not allowed to modify anything forward of the factory cats. Also, the cats need to be as close to the engine as possible to stay hot enough to be functional.
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      09-11-2018, 11:12 AM   #3
TemjinX2
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i say get a intercooler, mhd tune, coils, and plugs first. The stock turbos are pretty small and you won't get much benefit for exhaust modifications other then the down pipes.

ferorcity02 is correct, only cat backs are carb legal long as there less then 90 decibels.
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      09-12-2018, 07:39 PM   #4
Twinning_N54
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When I had my Eclipse GSX, I had 3' downpipe, HFC, and cannon exhaust. All passed the visual and the sniffer. I was hoping to do the same here. I know the best location for the Cats is as close to the turbos/engine as possible for heat purposes. But I'm sure I can get away with a few more inches. I plan on covering the DP with a ceramic coating to move the heat into the cats...
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      09-13-2018, 09:43 AM   #5
TemjinX2
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The N54 doesnt really benefit much from a exhaust like running a 3" on a 4g63. BMW and Mercedes already has relatively optimized exhaust systems from the factory.

Other then the downpipe, you won't see much gains from modifiying the exhaust system unless your going single turbo and upgraded turbos.

A intercooler and tune will net more power then modifying the exhaust system.

Also your cars a 2009, so you should be on the star system not sniffer test. Long as you don't have any check engine lights and you pass visual you should be able to pass.

But it'll probably depend on how efficient your HFC cars because the dme monitors afr, but also how efficient the cat is performing and could throw a cel if the HFC is not meeting the dme expections.

Just saying your reinventing the wheel for really little gains other sound.
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      09-15-2018, 05:34 PM   #6
Twinning_N54
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Quote:
Originally Posted by TemjinX2 View Post
The N54 doesnt really benefit much from a exhaust like running a 3" on a 4g63. BMW and Mercedes already has relatively optimized exhaust systems from the factory.

Other then the downpipe, you won't see much gains from modifiying the exhaust system unless your going single turbo and upgraded turbos.

A intercooler and tune will net more power then modifying the exhaust system.

Also your cars a 2009, so you should be on the star system not sniffer test. Long as you don't have any check engine lights and you pass visual you should be able to pass.

But it'll probably depend on how efficient your HFC cars because the dme monitors afr, but also how efficient the cat is performing and could throw a cel if the HFC is not meeting the dme expections.

Just saying your reinventing the wheel for really little gains other sound.

Thank you for your honest input. I guess you guys are right. I still want to replace the 2nd cats to HFC (instead of deleting them) and replace the catback pipes since they have alot of restricting bends.

thanks for everyone input, Ill spend the rest of my budget on an intercooler
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