PRIMARY / SECONDARY CAT REMOVAL need advice who has done it

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ray d

Active Member
Joined
Jul 4, 2012
Messages
81
Location
Northern Ireland
Car
slk 55 amg
Hi I bought the front pipes to take out the secondary cat and opened it up today and I thought the car had sucked in a pussy cat as all is in it is hair. I am doing it to get a bit more of V8 noise but am now wondering if I have wasted my money. Is there anyone who has removed the "cat hair" and has it made the noise any better. I have already put in a "x" pipe. All the hair out and there is a pipe going straight throu with holes in it. Do I leave that in or what. Will it help get the noise out that I know is in there somewhere. Has anyone removed the main cat and is there any problem as there is a sensor in that one. Thanks for any help. :(:(:(
 
Hair? Should be a cordierite monolith in a catalytic convertor. - A pre-cat might be kanthal as that tends to run at higher temperature.

You haven't opened up the resonator have you? Fibreglass matting is often used as sound deadening in mufflers.
 
Sounds like you've opened up the wrong box. I've had both out on mine primary's and secondary's and there certainly wasn't any fibreglass ( hair looking ) stuff in sight.
 
No I took the resonator out and replaced it with the x pipe. Opened the last box on the front pipe (main cat just below the header with the 2 sensors and then the round box about the size of 2 bean tins end to end) just before the joint. Cant remember if my 171 was loke this but perhaps I should have said this is the 172
 
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I get a couple of different catalysts for analysis throughout the year (usually LNT or DOC) and they're always ceramic monolith or Kanthal. - Admittedly that's not the full range of catalysts in use, but our customers have never asked about analysing fibrous material.
 
I took the cats out of one of my TVR.s and it was like a honey comb and that is what I was expecting but when I cleared the hair out of this it has a pipe with holes in it and you could put a screw driver handle right throu it from one end to the other so it is def not a cat. I am surprised no one else has spoken about this.It has to be some sort of muffler but why Merc have fitted it is beyond me
 
When you take your car in for MOT, and the tester looks at it,, only to find you have no cat ,,then he just might fail it . If it should have a cat ,this is sorted out by the year of the car and when it was made.
 
Are you sure the existing exhaust is original factory fit? Sounds like someone's been there before you?
 
P1110838.JPG

I am sure it is standard, I have checked it with the one on the car, I have not touched the main cat due to the MOT in a few years. Everybody talks about the sec cat is for emissions in the USA. here is a pic of the "thing" cut open. I am prity sure you will not see the opening when re welded as it is on the top
 
That's definitely a silencer. - As above, I'd guess that someone has already replaced the catalytic convertor with a silencer.
 
When you take your car in for MOT, and the tester looks at it,, only to find you have no cat ,,then he just might fail it . If it should have a cat ,this is sorted out by the year of the car and when it was made.

Technically yes. In reality, if it doesn't fail the emissions there's no reason to look any closer at the exhaust (other than to check for leaks).
 
Sorry to hi jack. Where is the best place to get the x pipe? Ta.
 
I got ""x pipe from power flow, The "thing" is def standard, I have checked it with the original one still in the car even down to the letters and numbers on box and I just know by the welds etc it had not been touched. I am surprised that no one has come across this before. It would be interesting to here from someone who has done the same. I am wondering if the 171 has a sec cat and the 172 does not. Perhaps Mr Merc put another muffler in encase any lady hairdressers would not like the noise (now if I got a £1 for every time someone told me it was a hair dresser's car) hmmmmm
Anyway I have it all welded up again and am hoping to get them in tomorrow.
 
I had the secondary cats gutted on my C55 Wagon. When opened up (in situ) they contained a grey honeycomb that came out like crumbled breeze-block dust. This was achieved with an electric drill, shoved in through the opening.

I have never had an issue with an MOT and nor would I expect to? The cats are still there (in looks) and the car passes emissions without any concern. The tester has no reason to go further and certainly cannot open up the box - welded or not..
 
Getting the better of me so googled the numbers on box
Mainly on German sites but it is a cat but it is not what I expected.
Perhaps a secondary does not have to catch as much what ever they catch as a primary cat does (am guessing now but at least I know it is a cat) :bannana::bannana::bannana::bannana:

Mercedes-W172-R172-SLK-55-AMG Catalyst Cat. No. A1724900601
Zum Heranzoomen mit der Maus über das Bild fahren
Mercedes-W172-R172-SLK-55-AMG Catalyst Cat. No. A1724900601
Mercedes-W172-R172-SLK-55-AMG Catalyst Cat. No. A1724900601
 
That part no does not show up on the EPC--- this often happens with exhaust components which are numbered but are not available as discrete spare parts -only as part of complete assemblies. This would indicate that said assemblies are indeed genuine but altho called "secondary catalysts" their internal construction would indicate they are straight thro glass pack silencers
https://en.wikipedia.org/wiki/Glasspack
designed to reduce back pressure rather than reduce noise.

http://www.rodsnsods.co.uk/forum/tech-features/home-made-glass-packs-mufflers-49122
 
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This thread shows the internal construction of a normal non straight thro silencer with pictures.
Sorry its from a BMW
https://www.bimmerforums.com/forum/showthread.php?1952841-z3-exhaust-mod

13+-+8


13+-+5
 
That will be a lot of welding to seal that one up. Have just stopped for a "coffee fix". 1 in 1 to go. Thankfully the header to down pipe bolts have loosened
 

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