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#1 Old 09-18-2013
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Question SLK55 secondary cat upgrade

Hi all:

After reading about the cat setup in the SLK55 here and elsewhere, I've been considering replacing the secondary cats as I've heard they're rather restrictive 300 cell ceramic ones.

Magnaflow makes a 200-cell spun metallic cat that I've been looking at, but I wanted to double-check with you guys to see if that'd be a suitable replacement. I'm a newbie when it comes to exhaust stuff, so I appreciate any help or advice you can offer. (The forum already proved helpful when I was considering removing my resonator. I did, and installed a Magnaflow X-pipe that was mentioned here, and it sounds *great*!)

Thanks!

-Rob
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#2 Old 09-20-2013
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Originally Posted by ThinkRob View Post
Hi all:

After reading about the cat setup in the SLK55 here and elsewhere, I've been considering replacing the secondary cats as I've heard they're rather restrictive 300 cell ceramic ones.

Magnaflow makes a 200-cell spun metallic cat that I've been looking at, but I wanted to double-check with you guys to see if that'd be a suitable replacement. I'm a newbie when it comes to exhaust stuff, so I appreciate any help or advice you can offer. (The forum already proved helpful when I was considering removing my resonator. I did, and installed a Magnaflow X-pipe that was mentioned here, and it sounds *great*!)

Thanks!

-Rob
I removed the primary cats (assuming they're primary since they come right off the engine) and put straight pipes that look like cats in their place. Sound is amazing and I get a lot of compliments on it. Smells a bit rich, but the tune is good and the data logs are good. Plus I'm still able to go down my street at 2AM and not wake up the neighbors if I don't want to.
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#3 Old 09-20-2013
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Originally Posted by thirteendog View Post
I removed the primary cats (assuming they're primary since they come right off the engine) and put straight pipes that look like cats in their place. Sound is amazing and I get a lot of compliments on it. Smells a bit rich, but the tune is good and the data logs are good. Plus I'm still able to go down my street at 2AM and not wake up the neighbors if I don't want to.
Ok. But I'm afraid that's not really what I'm after.

I'd really rather not break the law (which I'm pretty sure removing the primaries would), plus I don't really want my car to be any louder than it is.
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#4 Old 09-20-2013
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Come to the SLK cookout in North Myrtle Beach, on September 21 at 1 PM. There you can hear a 55 with X pipe and secondary Cats removed. You can judge the sound level for yourself.
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#5 Old 09-20-2013
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#6 Old 09-21-2013
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Originally Posted by Elbert55 View Post
Come to the SLK cookout in North Myrtle Beach, on September 21 at 1 PM. There you can hear a 55 with X pipe and secondary Cats removed. You can judge the sound level for yourself.
I agree with this!
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#7 Old 09-21-2013
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Damn. I missed this post! Well... I guess I'll have to hang around for another year.
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#8 Old 09-21-2013
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Quote:
Originally Posted by ThinkRob View Post
Damn. I missed this post! Well... I guess I'll have to hang around for another year.
ThinkRob,
I am in Winston-Salem. When you get your 15 posts on the forum, message me and we'll work something out about getting together.
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#9 Old 09-23-2013
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Will do.

I'm still trying to figure out whether I even need the secondaries for NC inspections...
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#10 Old 09-23-2013
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We hope to have a meet in November in the North Myrtle Beach area.
email [email protected]

He will add you to our email list for info on future meets. See pictures of this past meet at

https://www.slkworld.com/u-s-southeas...tml#post859554

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#11 Old 09-28-2013
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Done. Still looking for an answer on whether those would be suitable secondaries though. It looks like I'm going to have to go the upgrade route, since none of the welding shops around here will even think about removing them altogether...
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#12 Old 09-30-2013
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You are correct. No Retail shop will touch it.
PM
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#13 Old 11-09-2013
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Quote:
Originally Posted by Elbert55 View Post
You are correct. No Retail shop will touch it.
PM
I'm back to my original question.

From what I recall, the exhaust has a near-90-degree bend right after the secondaries. Would it be possible to remove the OEM ones, reduce the bend, and put the Magnaflow cats that I linked to further down the line, maybe on a straight section? (I'd like to get rid of the bend/flow reduction if possible...)

Or, if that's a bad idea, will they fit in the space that the existing secondaries need?

Last edited by ThinkRob; 01-24-2014 at 05:56 PM.
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#14 Old 11-09-2013
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The secondary cats are just resonators aren't they? At least that's what they were when I had all 4 cats removed off my SLK350. The front cats had the converter material inside them. The rear cats had nothing. I think most people just replace the secondary cats with straight pipes or replace the secondary cats with performance cats and deleting the front cats?


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