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C55 | Removed secondary cats and resonator - sounds amazing!

Old 01-10-2019, 05:06 PM
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C55 | Removed secondary cats and resonator - sounds amazing!

Finally pulled the trigger on getting my secondary cats out, and holy sh#t, it's amazing. The exhaust note sounds throatier and much meaner. There are also more pops and gurgles, especially when the rpms are coming down from the overrun. I can't believe I waited this long to do it! I won't say which shop did this, but I paid $250 out the door.


Dropped off my Eurocharged Headers on the way back up to SF to get ceramic coated at a place called Accessories Plus in Belmont, CA. They have a great shop, and the owner Steve is a really great guy. $220 for ceramic coating. Will post a video when I get those on as well.
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Old 01-10-2019, 10:12 PM
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Just in time for the new california exhaut law lol.
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Old 01-10-2019, 11:35 PM
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Lol I know FML. It's not THAT loud... Only when I step on it.
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Old 01-11-2019, 12:16 AM
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I'm glad you mentioned the CA muffler law - I didn't know anything about it. It doesn't sound like anything actually changed, just another cash grab. It's a little more clear now though.

A few years ago (maybe 10?) it took me the good part of a day to even figure it out because the Vehicle Code only referred to some ASTM test standard, which then referred to an ASTM test procedure (neither of which were free for download). The long and short of it - for at least 10 years, the CA exhaust noise standard has been 95db. The way it is measured (which was never clear until I researched it and I doubt many cops even know) is that it may not exceed a PEAK of 95db (A weighted) at ANY RPM at a 45 degree angle at round 30" from the exhaust tips and 12" from the ground. That's 60% of the stock performance cars on the road. Just an excuse to fine anyone with any kind of exhaust mods. I highly doubt they will enforce a fine against anyone who is actually stock unless they are a nuisance.

Sucks because I have an X pipe ready to go. I just wasn't going to remove my secondaries. Just another reason to flee the sinking ship that is CA...

Last edited by Spooky55; 01-11-2019 at 12:18 AM.
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Old 01-11-2019, 12:39 PM
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Spooky55......

What effects do you think removing the secondary cats will have on your next CA smog test renewal?

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Old 01-12-2019, 12:40 AM
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I am very leery of removing the secondaries in CA, restrictive as they may be. It won't affect the OBD-II portion of the test by throwing codes since they are well downstream of any sensors, but it will most likely fail on visual inspection.

I'm leaving mine in place and installing the X pipe in place of the resonator. At least that will get rid of the most restrictive section of the exhaust. Not as much benefit, but much less risk of failing smog.

rilonprime: How is your car at cruising speed now? Does it drone? I drive a lot of highway miles, so drone can get annoying.
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Old 01-12-2019, 01:02 AM
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Spooky55........

I've owned the car since August 2006 and I just don't notice any drone at all! However, since I added Eurocharged shorties and ECU tune two years ago, the sound difference has been pretty amazing and exciting under load! I've done all I want to do to it! Almost bought a '08 Clk63 AMG Black Series in November but the seller really misrepresented the condition of the car! It cost me $1,000 for travel to Portland Oregon and a PPI (Pre-Purchase Inspection) and I was really disappointed I didn't get to drive it home! In this case, I let my head rule my heart! lol.......C'est la Vie!

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Old 01-12-2019, 01:48 AM
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Damn, a CLK63 Black Series is a special horse. Would love to drive one.

Spooky: the previous owner had already deleted the resonator before I got the car, and I was a little disappointed that there was some drone around 2200 - 2500 RPMs, but to be honest I got used to it.
​​I am generally pretty picky when it comes to noises (I dynomatted my trunk and door panels to try and lower the road noise), and I can say that this mod has definitely made the exhaust louder, but there is no more drone than before.
From what I've done to Mercedes before, I would consider KEEPING the stock resonator (they aren't that restrictive, and are pretty high quality) and removing the secondaries. The exhaust note and burbles were definitely worth getting rid of the secondaries, and I'm already on my second tank of gas since the "operation" because I've been driving a little heavy-footed. If you're ever in San Francisco let me know and I can give you a ride to see if you like it or not.
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Old 01-12-2019, 11:15 AM
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Rilonprime....

Thanks for the invite! I've got quite a few friends living in and around SF for decades and they tell now me that they avoid going downtown due to the "increased homeless and crime activity"! I've also spent a lot of time working in downtown SF and its a crying shame that City leaders won't get of their collective asses and fix the problem!

Rob
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Old 01-13-2019, 01:06 AM
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Thanks for the info on drone. I wonder if there is a different resonator (maybe for an M113k car) that has dual in and dual out? The cats are always a huge damper on sound, regardless of flow capability. The resonator is supposed to kill the drone. As nice as the car sounds with cat and resonator delete (it sounds great!), I'm mostly interested in power (and apparently have to be more careful about the quest to have it sound good).

Speaking of which, I was going by memory on the testing they use for determining compliance and was a little off. Apparently they measure 19" from the tips, but only at idle and 2500 rpm. Here is a great YouTube video on AB 1824:

For whatever reason, the stock C55 exhaust is all over the place. I put a caliper on it to see what size x pipe I should get and the design is crazy:

2.5" before the secondaries, then 2.3" after the secoundaries and into the Y pipe to a pathetic 2.7" SINGLE PIPE through the resonator and back out to 2" duals to the mufflers.

So if you look at flow, that's 9.81"^2 before the cats to 8.31"^2 after AND THEN DOWN TO 5.72"^2 through the resonator, then back out to 6.28"^2 to the mufflers. See why I want to get rid of the resonator?

Intake and exhaust seem to the best power adders for these cars. This seems to be the worst part.
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Old 01-13-2019, 10:46 AM
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C55 AMG Touring with Kleemann headers, ECU and TCU: 414 hp and 576Nm :-))
Primary cats most restrective on the exhaust side. I have Kleemann headers with oem secondaries. Remember asking them what would happen
if I changed the secondaries to Kleemann sportcats and the answer was that nothing really would change regarding power.
Other members here on mbworld have confirmed this.
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Old 01-14-2019, 02:46 AM
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Originally Posted by amgen View Post
Other members here on mbworld have confirmed this.
A member proved there was a power benefit to removing the secondaries, with Dyno figures. I tend to believe data over speculation.

https://mbworld.org/forums/c32-amg-c...oved-dyno.html


I've noticed the exhaust is not as "wheezy" when reving in park than it was with the secondaries. I wonder if this is because there is less obstruction, but this is just an observation.

The sound alone was worth it for me. Any louder and it would probably be unbearable, so besides the new headers I won't be modifying it any further.
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Old 01-14-2019, 08:10 AM
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I figured leaving the secondary cats was sacrificing horsepower, but that is surprising - 13hp and 19tq is quite a lot.

I will have to do that if I ever get out of CA. Car is my daily driver so I can't afford to have it fail smog or have an uncorrectable violation. I'll have to be satisfied with the gains produced by eliminating the resonator and continuing the dual exhaust all the way out. It would have to equal or exceed that or removing the secondaries.

This will reduce low rpm torque somewhat, but the x pipe is designed to mitigate that and still gain horsepower in the higher rpm range. I just won't have that awesome growl that will likely get me cited.
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Old 01-14-2019, 12:58 PM
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Originally Posted by Spooky55 View Post
I figured leaving the secondary cats was sacrificing horsepower, but that is surprising - 13hp and 19tq is quite a lot.

I will have to do that if I ever get out of CA. Car is my daily driver so I can't afford to have it fail smog or have an uncorrectable violation. I'll have to be satisfied with the gains produced by eliminating the resonator and continuing the dual exhaust all the way out. It would have to equal or exceed that or removing the secondaries.

This will reduce low rpm torque somewhat, but the x pipe is designed to mitigate that and still gain horsepower in the higher rpm range. I just won't have that awesome growl that will likely get me cited.
The guy had headers on as well which he only clarified later on in the thread.

That whole thread was a mess reading it. The guy claims huge numbers by just removing cats than later in the thread comes in and says oh I had headers on and a BMW M5 exhaust :/
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