W204 C63 - Secondary Cat Delete or Remap first?

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So after another drive, I don't think I have the patience to wait to do the exhausts. from all my research I have narrowed it down to Milltek straight pipes, remove second cats with MSL or gut the secondary cats. Would MSL also go cat gut removal?

Noise wise all sound very similar so any final input from anyone would be great, just can not decide:)

Many thanks

Rich
 
MSL will gut the cats if that is what you want. I'd just remove them completely and
get the remap afterwards and save another trip;)
 
Best not remove them, Just gut them as there is mot changes coming and gutting means you cant see anything.
 
^ The changes in the MOT rules for cats has been in place for a long time.
It's the diesels they are after now with DPF removal meaning a fail.
 
This is what worries me, I don't have a friendly MOT station, (what I mean is I just don't know them as I have never had a car MOT) so is it better to appear standard and get the same sound and not have to worry?
 
The 1 thing about mot testing stations is, yes your c63 is supposed to have 4 cats and if 2 are removed its an mot fail “only if the tester knows they are missing” so go to merc and it will def fail, go to a non merc garage that doesn't know, the tester will look for the presence of cats, tick can see the 2 in the downpipes, tick it passed its emissions test, tick passed its mot. Btw that is the correct test procedure outlined by the dvsa
 
Remove the secondary cats, its easy, cheap and sounds superb, not too loud and NO rasp, Get them gutted, not removed,

My last C63 with the secondary cats gutted.

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What does it involve to gut the secondary cats?
 
Hi Andy

It requires the exhaust section containing the Secondary Cats to be removed, you then need remove the material which is contained within the Cat by one means or the other, I used a giant screw driver and a hammer. Didn't damage the Cat at all, but removed everything within a few minutes.

It depends how easy it is to get into the cat to ensure you remove every little bit of the decat material, which resembles a honeycomb.

Here is a pic of when I gutted a pair of Audi V8 cats, and the material you need to remove, it then leaves the cat totally empty and the exhaust gasses simply flow through the original cat, which now has the restriction removed.

You need to ensure your wearing gloves and something to prevent you inhaling the dust, as this is hazardous and why many people just removed the cat in it's entirety.

The Audi Cat was easy to gut, as it was located at the end of a downpipe section, so was easy to see what you were doing and ensure that every little bit was removed





You should end up with a bin liner full like this. (Note - There are normally some spring looking rings that assist in retaining the honeycomb content in the event that the material starts to break up when in normal use, I'm not sure if Mercedes cats have these, but that's why it's important to be able to see what your doing.



I found it easiest just to get MSL to simply remove the entire cat and replace the section with a straight through section. They do a great job and unless an MOT Tester was very familiar with C63's they wouldn't even spot that the secondary cat had been removed, the quality of MSL's work leaves a perfect finish.

Mine passed it's MOT at Mercedes and they didn't realise it had both secondary CATs removed and it passed the emissions test with no problem.
 
Yup, as above but when i have my three sets done i just had them gutted then you dont have to worry about the whims of a mot tester or changing specs for mots.
 
Hi Andy

It requires the exhaust section containing the Secondary Cats to be removed, you then need remove the material which is contained within the Cat by one means or the other, I used a giant screw driver and a hammer. Didn't damage the Cat at all, but removed everything within a few minutes.

It depends how easy it is to get into the cat to ensure you remove every little bit of the decat material, which resembles a honeycomb.

Here is a pic of when I gutted a pair of Audi V8 cats, and the material you need to remove, it then leaves the cat totally empty and the exhaust gasses simply flow through the original cat, which now has the restriction removed.

You need to ensure your wearing gloves and something to prevent you inhaling the dust, as this is hazardous and why many people just removed the cat in it's entirety.

The Audi Cat was easy to gut, as it was located at the end of a downpipe section, so was easy to see what you were doing and ensure that every little bit was removed





You should end up with a bin liner full like this. (Note - There are normally some spring looking rings that assist in retaining the honeycomb content in the event that the material starts to break up when in normal use, I'm not sure if Mercedes cats have these, but that's why it's important to be able to see what your doing.



I found it easiest just to get MSL to simply remove the entire cat and replace the section with a straight through section. They do a great job and unless an MOT Tester was very familiar with C63's they wouldn't even spot that the secondary cat had been removed, the quality of MSL's work leaves a perfect finish.

Mine passed it's MOT at Mercedes and they didn't realise it had both secondary CATs removed and it passed the emissions test with no problem.


Cheers Jim. Looking forward to seeing how yours goes and sounds with the delete done :)
 
Hi - can you just buy a swap-out section of pipe that bolts into place? I would like to remove my 2nd Cats too but I want to return them to standard if I sell the car. I've heard that a piece has to be CUT out so it seems rather "final"?
Thanks
 
Cheers Jim. Looking forward to seeing how yours goes and sounds with the delete done :)
The secondary delete offers next to no improvement on power. It was in for US anti smog laws.

Get it whipped out then mapped though - thats the best way.
 
Doing away with secondary’s didn’t really make a great deal of difference at all to be honest. Even the exhaust note doesnt change that much. It’s only when you punch it you notice the difference in sound but not much. Like said no difference power wise. Obviously this is keeping resonator in place.

But!! When i had the primary’s removed as well its another story lol.
 

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