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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > Gutting secondary cats?!



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      07-23-2014, 04:31 PM   #1
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      07-23-2014, 04:36 PM   #2
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I haven't personally done it,but from other threads in this section learned that you get some more cabin noise as well although it is said to not be so intrusive. As for the sound, the resonator is what muffles a lot of the sound on the stock exhaust and removing that will give you a much more louder exhaust.
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      07-23-2014, 10:40 PM   #3
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I just had mine deleted due to one of them was rattling at idle. The exhaust tone is almost factory until you get to about 70 -75 mph. You then hear a little rumble, I'm talking about inside the vehicle, A/C on, and windows up.
On the outside of the vehicle, my friend tells me that my exhaust is a little raspier now. I have read some peoples posts, that say secondary cats and resonator delete, give them the sound they are looking for. Muffler delete is F@#king LOUD, I already made that mistake once. Lasted 24 hours, and I re-installed my muffler.
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      07-24-2014, 12:45 AM   #4
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Do it right and remove the whole section for best results.
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      07-25-2014, 10:46 AM   #5
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Quote:
Originally Posted by TheAxiom View Post
Do it right and remove the whole section for best results.
Think it's possible to put the gutted cats back on over straight pipes welded in for a stealth install?

I just want to pass visual inspection.
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      07-25-2014, 11:32 AM   #6
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Quote:
Originally Posted by Dylanize View Post
Think it's possible to put the gutted cats back on over straight pipes welded in for a stealth install?

I just want to pass visual inspection.
Absolutely. The issue with the "gutted cat" vs a straight pipe is the flow characteristics of an empty chamber. My understanding is it can actually hurt power overall.
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      07-25-2014, 12:05 PM   #7
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Quote:
Originally Posted by TheAxiom View Post
Absolutely. The issue with the "gutted cat" vs a straight pipe is the flow characteristics of an empty chamber. My understanding is it can actually hurt power overall.
thats always been mine too. I wouldnt do it unless you can get the shell of the cat welded or secured to the stright pipe you would be replacing it with.
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      07-25-2014, 06:20 PM   #8
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Quote:
Originally Posted by Dylanize
Quote:
Originally Posted by TheAxiom View Post
Do it right and remove the whole section for best results.
Think it's possible to put the gutted cats back on over straight pipes welded in for a stealth install?

I just want to pass visual inspection.
I don't think you'll fail inspection if you remove secondary cats. 330 n52 doesn't have secondary cats at all, right? I thought I only primaries are required. At least here in maine.

I'm thinking about doing the same. Res and sec cat delete. I've done muffler delete before and droned too much. I just don't wanna have to put them back on cause it drones. I rather spend a little extra and have it right. Not $1000 though.

Does anyone know how loud res and sec cat delete is compared to pe?
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      07-26-2014, 10:37 PM   #9
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Quote:
Originally Posted by new_username View Post
I don't think you'll fail inspection if you remove secondary cats. 330 n52 doesn't have secondary cats at all, right? I thought I only primaries are required. At least here in maine.

I'm thinking about doing the same. Res and sec cat delete. I've done muffler delete before and droned too much. I just don't wanna have to put them back on cause it drones. I rather spend a little extra and have it right. Not $1000 though.

Does anyone know how loud res and sec cat delete is compared to pe?
My guess is not as loud as the PE because the stock muffler is not designed to make a lot of noise. Very interested to hear what this set up sounds like though.
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      07-27-2014, 12:47 AM   #10
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Quote:
Originally Posted by TheAxiom View Post
Absolutely. The issue with the "gutted cat" vs a straight pipe is the flow characteristics of an empty chamber. My understanding is it can actually hurt power overall.
I made a cut after the 2ndary cats, took out the filling and placed a clamp over the cut. It's been like 5k miles on since then? No issues with my throttle/pressure loss (butt dyno) but I'll get an official dyno maybe this week.

To me, the exhaust has only one exit, it's not like it's making it's own tornado in the shell. Still looks stealthy.
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      08-02-2014, 01:16 PM   #11
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      08-02-2014, 01:35 PM   #12
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just buy some aFe race pipes, they sound great paired with my PE. I'd rather install new pipes than mess with the factory ones..
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      08-02-2014, 01:54 PM   #13
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Some guys leave the secondary cats on because they have catless headers. I guess it helps with emissions. If you're planning on getting headers, you may want to leave them on
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