2nd cat delete
Thread Starter
Junior Member
Joined: Apr 2014
Posts: 30
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2010 White C300 Sport
2nd cat delete
I wanted more sound from my c300, so i put an x-pipe in. I loved it but i wanted more, got the mufflers removed, hated the sound, sounded like a beat up ghetto civic, so i put them back on, but now i've done more research into removing the 2nd cat, but i'm kinda confused on what exactly that is.... Is there a difference between the catalytic converters than the secondary catalytic converter? Please explain, because I plan on going to the shop to get an estimate, and I wanna tell the guys to remove the correct part.
Thanks!
Thanks!
Senior Member
Joined: May 2014
Posts: 314
Likes: 15
2016 GLE450 AMG Coupe
I wanted more sound from my c300, so i put an x-pipe in. I loved it but i wanted more, got the mufflers removed, hated the sound, sounded like a beat up ghetto civic, so i put them back on, but now i've done more research into removing the 2nd cat, but i'm kinda confused on what exactly that is.... Is there a difference between the catalytic converters than the secondary catalytic converter? Please explain, because I plan on going to the shop to get an estimate, and I wanna tell the guys to remove the correct part.
Thanks!
Thanks!
MBWorld Fanatic!
Joined: Aug 2010
Posts: 1,020
Likes: 0
From: New York
2010 c350
Keep your mufflers, cut secondary cars and put x-pipe in there place. The x pipe should be as far up as possible after the primaries. You will need to add bungs into the exhaust piping and good quality elbows in order to screw your downstream 02 sensors in. If you don't do this your car will run with check engine light and you will not pass inspection. If you do decide the remove the secondary cats you will lose low end torque and back pressure so I don't recommend it on a stock vehicle. If sound is your main concern than she'll out the extra cash and get a new exhaust system entirely like a meistershaft or another axle back system. Once you start playing with cats things get really hairy if you don't fully understand how exhaust works, believe me I've been through it and I'm still working things out. Hope this helps.
Thread Starter
Junior Member
Joined: Apr 2014
Posts: 30
Likes: 0
2010 White C300 Sport
Keep your mufflers, cut secondary cars and put x-pipe in there place. The x pipe should be as far up as possible after the primaries. You will need to add bungs into the exhaust piping and good quality elbows in order to screw your downstream 02 sensors in. If you don't do this your car will run with check engine light and you will not pass inspection. If you do decide the remove the secondary cats you will lose low end torque and back pressure so I don't recommend it on a stock vehicle. If sound is your main concern than she'll out the extra cash and get a new exhaust system entirely like a meistershaft or another axle back system. Once you start playing with cats things get really hairy if you don't fully understand how exhaust works, believe me I've been through it and I'm still working things out. Hope this helps.
Thread Starter
Junior Member
Joined: Apr 2014
Posts: 30
Likes: 0
2010 White C300 Sport
Keep your mufflers, cut secondary cars and put x-pipe in there place. The x pipe should be as far up as possible after the primaries. You will need to add bungs into the exhaust piping and good quality elbows in order to screw your downstream 02 sensors in. If you don't do this your car will run with check engine light and you will not pass inspection. If you do decide the remove the secondary cats you will lose low end torque and back pressure so I don't recommend it on a stock vehicle. If sound is your main concern than she'll out the extra cash and get a new exhaust system entirely like a meistershaft or another axle back system. Once you start playing with cats things get really hairy if you don't fully understand how exhaust works, believe me I've been through it and I'm still working things out. Hope this helps.
this is the kinda sound im going for.
Another thing: you said if i removed the 2nd cats, i would lose low end torque and back pressure, how much will that affect my car's performance speed wise? I know c300s aren't fast, but I definitely don't wanna make it any slower. Or is the loss of the low end toque not gonna be noticeable?
MBWorld Fanatic!
Joined: Aug 2010
Posts: 1,020
Likes: 0
From: New York
2010 c350
Quite a bit actually, your pickup would be bad, you may get a little extra hp but it would only be noticable over 80mph. You could always put in some universal mufflers. Remus makes some or you could go with magnaflow or something. Unless you plan on upgrading the headers I really don't reccomend removing any cats. The exhaust on German cars are built with back pressure in mind so unless you increase the amount of air coming in to the exhaust stream your just losing back pressure and therefore low end torque. Also just removing the secondaries won't do much for the sound other than make it louder. What you could do is swap out to new mufflers and swap your stock resonater with an x-pipe. It will give the car a slightly more exotic sound.
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Junior Member
Joined: Sep 2014
Posts: 33
Likes: 3
09 C300 Sport
Keep your mufflers, cut secondary cars and put x-pipe in there place. The x pipe should be as far up as possible after the primaries. You will need to add bungs into the exhaust piping and good quality elbows in order to screw your downstream 02 sensors in. If you don't do this your car will run with check engine light and you will not pass inspection. If you do decide the remove the secondary cats you will lose low end torque and back pressure so I don't recommend it on a stock vehicle. If sound is your main concern than she'll out the extra cash and get a new exhaust system entirely like a meistershaft or another axle back system. Once you start playing with cats things get really hairy if you don't fully understand how exhaust works, believe me I've been through it and I'm still working things out. Hope this helps.
Last edited by Synolimit; Nov 26, 2014 at 07:34 PM.
MBWorld Fanatic!
Joined: Aug 2009
Posts: 1,134
Likes: 8
From: Charlotte, NC
2015 BMW M235i 6MT
C300 Custom Exhaust - Cold Start - YouTube
this is the kinda sound im going for.
Another thing: you said if i removed the 2nd cats, i would lose low end torque and back pressure, how much will that affect my car's performance speed wise? I know c300s aren't fast, but I definitely don't wanna make it any slower. Or is the loss of the low end toque not gonna be noticeable?
this is the kinda sound im going for.
Another thing: you said if i removed the 2nd cats, i would lose low end torque and back pressure, how much will that affect my car's performance speed wise? I know c300s aren't fast, but I definitely don't wanna make it any slower. Or is the loss of the low end toque not gonna be noticeable?
Everything hitokiri89 says is true, but doesn't apply to our cars in the case of "2nd cats". What the W204 community calls our "2nd cats" are actually small "resonators". Being that they are actually resonators, deleting these will NOT result in a change in airflow causing a decrease in back pressure. It will ONLY result in a change of sound. (EDIT: hitokiri89 may have read your reply wrong, because it sounds like he is still talking about primary cats, whereas the question in your reply refers to "2nd cats".)
Anyways, my exhaust in that vid has the "2nd cats" deleted (replaced with straight pipes) and the center resonator deleted (replaced with a universal Magnaflow x-pipe). I would have liked the x-pipe to be placed in place of the "2nd cats", but there wasn't enough room. But honestly, there probably would have been no difference anyways.
You should totally do this mod! Adds a lot of character to the exhaust note. Lots of grumbles and gurgles at low speeds. It's loud, but it's nowhere near what I would consider obnoxiously loud.
MBWorld Fanatic!
Joined: Aug 2010
Posts: 1,020
Likes: 0
From: New York
2010 c350
I actually did mean the secondaries, and they are cats being that take read an 02 signal that's reported back to your cars computer. If you remove them you will have a two less obstacles in the way of your exhaust flow, which will result in a loss of low end power. You may have increased power under wot but only at the high rpm and at higher speeds like on the highway. Trust me, removing them is a pain in the *** if you plan to pass inspection. You need is tall bungs to accept the 02 sensors of you do. I'm talking from experience, I just don't want anyone to have to go through the same bs I had to. The c300 is low on power to begin with, why decrease your performance for sound ? If your going to play with cats then just do the whole exhaust. At least that way you'll gain a few hp to balance everything out. Also you might want to get a tune as well so it will be running properly.
Senior Member
Joined: Dec 2010
Posts: 440
Likes: 1
From: Dix Hills
2011 c300 4matic
I have magna flow race mufflers connected to an x pipe connected to a secondary cat delete
- there is drone
- it has a deeper sound to it
- it has a nice scream at the higher rpm
- you pass inspection fine since the O2 sensors are in the primary cats.
- does not sound similar to a straight piped c300
- there is drone
- it has a deeper sound to it
- it has a nice scream at the higher rpm
- you pass inspection fine since the O2 sensors are in the primary cats.
- does not sound similar to a straight piped c300
MBWorld Fanatic!
Joined: Aug 2009
Posts: 1,134
Likes: 8
From: Charlotte, NC
2015 BMW M235i 6MT
I actually did mean the secondaries, and they are cats being that take read an 02 signal that's reported back to your cars computer. If you remove them you will have a two less obstacles in the way of your exhaust flow, which will result in a loss of low end power. You may have increased power under wot but only at the high rpm and at higher speeds like on the highway. Trust me, removing them is a pain in the *** if you plan to pass inspection. You need is tall bungs to accept the 02 sensors of you do. I'm talking from experience, I just don't want anyone to have to go through the same bs I had to. The c300 is low on power to begin with, why decrease your performance for sound ? If your going to play with cats then just do the whole exhaust. At least that way you'll gain a few hp to balance everything out. Also you might want to get a tune as well so it will be running properly.
Newbie
Joined: May 2020
Posts: 1
Likes: 0
w204 c300
This is my car!
Everything hitokiri89 says is true, but doesn't apply to our cars in the case of "2nd cats". What the W204 community calls our "2nd cats" are actually small "resonators". Being that they are actually resonators, deleting these will NOT result in a change in airflow causing a decrease in back pressure. It will ONLY result in a change of sound. (EDIT: hitokiri89 may have read your reply wrong, because it sounds like he is still talking about primary cats, whereas the question in your reply refers to "2nd cats".)
Anyways, my exhaust in that vid has the "2nd cats" deleted (replaced with straight pipes) and the center resonator deleted (replaced with a universal Magnaflow x-pipe). I would have liked the x-pipe to be placed in place of the "2nd cats", but there wasn't enough room. But honestly, there probably would have been no difference anyways.
You should totally do this mod! Adds a lot of character to the exhaust note. Lots of grumbles and gurgles at low speeds. It's loud, but it's nowhere near what I would consider obnoxiously loud.
Everything hitokiri89 says is true, but doesn't apply to our cars in the case of "2nd cats". What the W204 community calls our "2nd cats" are actually small "resonators". Being that they are actually resonators, deleting these will NOT result in a change in airflow causing a decrease in back pressure. It will ONLY result in a change of sound. (EDIT: hitokiri89 may have read your reply wrong, because it sounds like he is still talking about primary cats, whereas the question in your reply refers to "2nd cats".)
Anyways, my exhaust in that vid has the "2nd cats" deleted (replaced with straight pipes) and the center resonator deleted (replaced with a universal Magnaflow x-pipe). I would have liked the x-pipe to be placed in place of the "2nd cats", but there wasn't enough room. But honestly, there probably would have been no difference anyways.
You should totally do this mod! Adds a lot of character to the exhaust note. Lots of grumbles and gurgles at low speeds. It's loud, but it's nowhere near what I would consider obnoxiously loud.
Hi,
does anyone know if removing the secondary catalytic converter will trip the check engine light?
