C32 de-cat

[Dizwen]

worth doing?

I know it a quick and cheap mod, better sound and a small performance gain but will the cars ecu need mapping? and how does it affect a MOT?

I await your collective wisdom!

 

[brucemillar]

I did it on my C55. I am not sure about your set up. But assuming you have 4 cats & a resonator? The remove the secondary cats and the resonator. If you have the cats opened with a disc cutter and the innards scooped out, then welded back up MOT should be fine. Do the same with the resonator. No ECU issues. Just a straight forward removal. On the 55 it gives it a much throatier sound and is louder at revs but not at cruising. So no booming on motorways or long drives.

 

[DRBC43AMG]

^ +1. No issues with ECU and gives a very nice sound

 

[Alex]

I replaced a pair of cats on my old ML55 with long downpipes. The lambda was at the threshold but passed the MOT.

 

[BTB 500]

There's no legal/mot issue with removing the resonator (centre muffler), so cleaner to replace it with a straight-though pipe than open it up and 'gut' it.

With the secondary cats 'gutting' is the safe route, however the general feeling seems to be that it will still pass an MOT ok with them removed completely (assuming the emissions are within limits). The new MOT regs only became effective in April and things are still settling down to a degree.

Obviously exhaust mods. should be declared to your insurer ...

 

[SavMan]

I don't know enough about the C32 setup but I doubt you will find any real change in performance. Most AMG exhausts have pretty good flow to start with and the bottle neck is typically the Primary Cats, if you are only removing the Secondary Cats you are only changing the noise (there maybe some small increase in flow but hardly noticeable). Removing them all would but you would be unlikely to pass your MOT.

If you goal is sound then you should be OK, there are quite a few modified C32's on here so they will hopefully be able to give you more first hand experience advice.

 

[kth286]

article in last week's Car mechanics mag had comments from VOSA.

If cat been removed from vehicle which qualifies for full cat test, then it should fail under section 7.1 (3).

So, suggest you look that up.

 

[BTB 500]

article in last week's Car mechanics mag had comments from VOSA.

If cat been removed from vehicle which qualifies for full cat test, then it should fail under section 7.1 (3).

So, suggest you look that up.

That's correct, but covers the situation where a car can meet the emissions with no cat at all (which some can).

Where a car has 4 cats to start with (2 primaries and 2 secondaries) and still has (just) the 2 primaries and still meets the emissions test is less clear cut though. Most testers are apparently saying this is fine since the car is still equipped with cats.

 

[DRBC43AMG]

The four cats design was to facilitate the engineering of exhaust so as to meet emissions in stringent areas of the world like California... where they also do a "visual" test

 

[BTB 500]

I was told it was to do with emissions shortly after startup - the smaller seconday cats reach working temperature faster