Have you failed MOT due to secondary cat delete?

Have you failed your MOT because of a secondary cat delete?

  • Yes

    Votes: 6 9.2%
  • No, passed without question

    Votes: 34 52.3%
  • No, i've got a 'friendly' tester

    Votes: 8 12.3%
  • Yet to find out

    Votes: 17 26.2%

  • Total voters
    65
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Had my CL500 for 6 years secondary cats removed never came close to failing on emissions which is what my local garage goes by.
 
Just to clarity for an ignoramus like me :) what are the secondary cats replaced with? X pipe? I just can`t get used to the quietness :(

Strictly speaking, no.

You typically remove the resonator and fit a X pipe or H pipe usually.

However, when you do that, there isn't a lot of room left as the CATs need room around them and get hot.

Solution to fit racing CATs with the same 200 cells as the secondaries (IIRC) or 100 cell ones.

My E always passed with no secondaries but never passed without primaries unless I went to a friendly MOT garage with Stevie Wonder doing the MOT.
 
Looks like my reading are a bit higher than yours but passed anyway. MOT this morning.

How timely :) much appreciated thanks. Bit higher yes, but still miles away from the limits.

Been intending to get the resonator replaced with straight pipes for years but now thinking a hidden gutting of the secondaries instead would be a better route.
 
Been intending to get the resonator replaced with straight pipes for years but now thinking a hidden gutting of the secondaries instead would be a better route.

I would do both. Your CLS would sound great having less silencing in the rear mufflers to my E55.
 
It is illegal. Fortunately, my MOT tester is only interested in the emissions of the car and has passed it 3 years running without secondary cats.:bannana:

You're MOT tester is only interested in the check he has to conduct in order pass or fail your car.

At the risk of doing him a disservice, he most likely has no actual knowledge of vehicle emissions, how they are produced in the engine, how they are managed by the exhaust after treatment system(s) or how they are measured in order to comply with prevailing regulation. He is certainly not equipped to carry out an emissions test, nor is he required to of course.

The MOT check doesn't even come close to a meaningful exhaust emissions test. That your car passes the MOT without secondary cats, fully illustrates the inadequacy of the method.
 
There's no box for 'my cars don't have cats' .
 
You're MOT tester is only interested in the check he has to conduct in order pass or fail your car.

At the risk of doing him a disservice, he most likely has no actual knowledge of vehicle emissions, how they are produced in the engine, how they are managed by the exhaust after treatment system(s) or how they are measured in order to comply with prevailing regulation. He is certainly not equipped to carry out an emissions test, nor is he required to of course.

The MOT check doesn't even come close to a meaningful exhaust emissions test. That your car passes the MOT without secondary cats, fully illustrates the inadequacy of the method.


Post #20 2nd image. Why would an MOT tester need any knowledge of vehicle emissions. He only has to hook the car up to a diagnostic machine which measures all the necessary emissions. Hardly his fault if the MOT test regulations don't meet the standard you feel they should. Mine passed, end of story.

If I thought I could get away with it, the primaries would go too and long tube headers would give me another 40+bhp.
 
You're MOT tester is only interested in the check he has to conduct in order pass or fail your car.

At the risk of doing him a disservice, he most likely has no actual knowledge of vehicle emissions, how they are produced in the engine, how they are managed by the exhaust after treatment system(s) or how they are measured in order to comply with prevailing regulation. He is certainly not equipped to carry out an emissions test, nor is he required to of course.

The MOT check doesn't even come close to a meaningful exhaust emissions test. That your car passes the MOT without secondary cats, fully illustrates the inadequacy of the method.

Post #20 2nd image. Why would an MOT tester need any knowledge of vehicle emissions. He only has to hook the car up to a diagnostic machine which measures all the necessary emissions. Hardly his fault if the MOT test regulations don't meet the standard you feel they should. Mine passed, end of story.

If I thought I could get away with it, the primaries would go too and long tube headers would give me another 40+bhp.

Suggest you read my post again. You clearly missed some salient points.
 
^ I re read your post and I'm not sure quite what point you are trying to make?

The car passed all the tests within the set parameters. As to whether the MOT comes close to a meaningful emissions test is neither here nor there currently.

As a diesel owner I think perhaps you should be more worried about emissions.
 
^ I re read your post and I'm not sure quite what point you are trying to make?

The car passed all the tests within the set parameters. As to whether the MOT comes close to a meaningful emissions test is neither here nor there currently.

As a diesel owner I think perhaps you should be more worried about emissions.

If your car has no secondary cats, the reality is it releases more CO, HC, NOx and Particulates at the tailpipe than my diesel.
 
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I would do both. Your CLS would sound great having less silencing in the rear mufflers to my E55.

Was the total stealth look that appealed rather than outright volume. If the increase was similar to just removing the resonator I think I'd be happy.
 
passed no issues, cans still in place but gutted inside
 
If your car has no secondary cats, the reality is it releases more CO, HC, NOx and Particulates at the tailpipe than my diesel.

I'm interested now. Do you make that assertion on the basis of particular research or evidence, or merely because your car meets the Euro 6 diesel standard? Go on; give us some numbers...
 
I've had the secondary cats removed with the X pipe installed and the SL55 passed the MOT last week. No issues from my side.

I assume you meant to say it passed the current emission test ? But if you are unlucky enough to get a pedantic or grumpy MOT tester your car would fail on the spot, 'clean' emission or, not simply due to the fact that you have physically removed the secondary (or even primary) cat(s) and the tester can fail it on that alone.

Going back to the OP's original question , and subsequent answers, it would appear that no one (yet) on this forum has been failed for the lack of secondary cats. So my guess is 99.9% of testers will go by emission output alone.
 
I'm interested now. Do you make that assertion on the basis of particular research or evidence, or merely because your car meets the Euro 6 diesel standard? Go on; give us some numbers...
Well, having spent more than 25-years in fuels R&D that included conducting full blown emissions testing on climate controlled chassis dynamometer systems with million dollar CVS emissions suites and having also conducted on-road and on highway emissions tests and bench tests on vehicles and engines from all of the major manufacturers, I could give you some numbers. But I'm not going to, you probably wouldn't believe me anyway.
 
Well, having spent more than 25-years in fuels R&D that included conducting full blown emissions testing on climate controlled chassis dynamometer systems with million dollar CVS emissions suites and having also conducted on-road and on highway emissions tests and bench tests on vehicles and engines from all of the major manufacturers, I could give you some numbers. But I'm not going to, you probably wouldn't believe me anyway.

So are the secondary CATs there to heat up primaries faster (by reducing flow) which is something I read once?

Or is it purely a case of filtering the exhaust a second time.

Or a combination?
 
For a catalyst to function, it has to reach a temperature above a certain point usually referred to as light-off and is about 500'C.

The small catalyst situated near to the engine (usually with 0.5m, sometimes directly attached to or even part of the exhaust manifold) is there to get catalytic conversion going quickly from a cold start. It warms up before the main catalyst a) because it's near the engine so the exhaust gas temperature is still pretty much as it left the engine and b) because it is smaller than the main catalyst and therefore has lower thermal inertia. However, it has nowhere near the internal surface area to perform successfully as the main catalyst.

The main catalyst situated further from the engine (though usually within a metre or so), also needs to get above about 500'C to start working. Being larger and further away from the engine means it takes a while to get up there. The internal surface area of the main catalyst is about the same as a football pitch which is enough to cope with the exhaust emissions over a wider operating range than the small catalyst.

Without the small catalyst, the car would typically fail a proper regulated emissions test due to emissions produced during the initial minute or two. Emissions over the rest of the cycle, i.e. once the main catalyst has warmed up would be fine. Would still pass the MoT though.

With just the small catalyst, the car would again fail a regulated emissions test. The initial emissions would be OK, but the car would be a 'gross emitter' overall. Would still probably pass the MoT, but out on the road with the engine under load, the tailpipe emissions would pretty much be as per engine-out.
 
On the E55K, the primaries come first within 0.5m of the engine. The secondaries are about a metre away.

How does this change things?
 

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