Decat headers exhaust . How are people getting away with it ?

1536Z4

1536Z4

Senior member
 North Shropshire
Site Supporter
Firstly let me point out that I have changed to hi flow cat exhausts on a previous car so I am not against changing them but they were emissions legal .

I see lots of You Tube posts of removing all the cats on headers / exhausts so how do they get away with it when it comes to MOT time or whatever it is called in the country the removal has been done .

Do they really go through the hassle of replacing the original headers/exhaust with cats before the test ?

I take it their insurance wouldn`t be covered ?

Is anyone on the forum running without cats that would like to enlighten me :poke:

Thanks :)
 
We have a tw@t in an M5 who spends most of his time on the limiter with no silencers and potentially no cats , driving/ drifting past my home. Weirdly he could drive past anyone in the county and we would still know he was there :x . Maye alright at the time I am at work, but early hours of a Saturday night its not. As for MOT, I know his mate runs a garage............ So, dodgy one every year. Dont mind a bit of sound, but this is ear bleeding loud.
Keep hoping to hear it scream and then a bang............ but those V8's seem pretty tough ..........
Some cars have primary and secondary cats , they remove just one set. I had a Focus ST 5 cyl and had a sports cat fitted to that. Was a 200 cell one, which meant it would be fine for MOT's and was remarked by my garage man as being spot on , even if I did a spirited drive to get it hot before the test.
I guess people just wing it for the year and bolt it in for the test. Not sure how many DPF's that have been gutted do get through the tests as well ?
 
Thrustyjust said:
Was a 200 cell one,
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Thanks for your reply and I can see you throwing a stinger out one night :rofl:

Hopefully he will drift it into a lamp post without injury of course and his insurance doesn`t pay out .

I had a 200 cell on my Saab and as you say they are spot on and within regulation . Dodgy MOT is probably the most popular as the MOT tester can just say it was ok when it was tested !!! I suppose it comes down to whether you want to take the risk .

DPF `s yes I bet there are loads of dodgy ones .

I can understand removing one set of cats as long as the remaining cats keep the emissions ok . If I could get a set of right hand drive headers with sport cats for the Z4 I would get them but not without cats . I think the only way I would get them is to have them custom made and that is way over my budget :)
 
1536Z4 said:
I see lots of You Tube posts of removing all the cats on headers / exhausts so how do they get away with it when it comes to MOT time or whatever it is called in the country the removal has been done .
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Very different rules for different countries. You would think for a country with a reputation as being 'clean/green' we would have strict rules on these things but we don't, mainly because of our older vehicle fleet (average 10 yrs old). So there is no emission testing at the WOF (MOT) stage, but various govt's have been trying to bring them in. Instead, the focus now seems to be getting people out of them, and into electric vehicles via rebate schemes etc. So to answer your question, as far as I'm aware I could cut out every cat on my car and as long as the exhaust doesn't smoke badly/visibly (which is a traffic offence liable to prosecution, but would have to be pretty bad to get pulled over) I won't get pinged on our WOF checks.
Because 95% of our cars are Jap imports they must be compliant with emission standards to be allowed to be imported, this just means that as long as the importer can show the data (from the manufacturer's emissions tests, e.g. that they meet ADR 79/01 and ADR 30/01, or Euro 4, or Japan 05, or US 2004) they are allowed into the country. I'm not 100% sure but I think they are then tested by the people who do the compliance checks at the border before they are allowed to be registered in NZ so they can say that the vehicle met standards at the time of import. After that it seems to be a bit loose as to what the owner can change on the exhaust.
Sorry for the long reply - it was exhausting...
 
enzed4 said:
it was exhausting...
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Now that does surprise me I would have thought that you would definitely had an emissions test . I suppose compared to the volcanic emissions it`s not worth testing for :lol:
 
Regarding a gutted DPF, this is from a respected MOT tester:
Emissions tests are only carried out on petrol engines vehicles. Diesel engines vehicles only have a metered smoke test, not a particulate test and as particulates are not tested, removal of the DPF should have little difference on the result.
 
Thrustyjust said:
eep hoping to hear it scream and then a bang............ but those V8's seem pretty tough ..........
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You should encourage him to Map it - it'll 100% pop then - they're well known to bend conrods when mapped :lol:
 
It all depends on how clued up the MOT tester is as they are supposed to visually check for missing/modified CAT's and other anti pollution devices.
The Police however are increasingly on the case and you run the risk of falling foul of the Construction and Use laws which carry far more serious penalties.
I'd be fairly confident in saying this is going to be a bigger issue for people every year as emissions rules are tightened further.
 
Zulu4 said:
Diesel engines vehicles only have a metered smoke test, not a particulate test and as particulates are not tested, removal of the DPF should have little difference on the result.
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I have a 55 plate 320d which was not produced with a DPF so was not aware that the emissions are not checked on cars with a DPF .

Are they supposed to check that a car that is supposed to have a DPF has one fitted for a MOT even it it has been tampered with ?
 
I thought it was now difficult to remove the DPFs and pass an MOT as if there is ANY smoke coming out of the exhausts at all its a fail.
 
Different engine but my E89 N20 2 litre 4 pot is decatted and the local garage has confirmed that the car will fail the MOT which doesn’t surprise me as it does stink when standing at traffic lights. The N20 unlike the 35i and 35is has only one cat and my intention is to refit the cat in October in prep for its MOT.

I’ve declared the remap, decat and suspension changes to my insurance company.
 
biZ4rreMids said:
my intention is to refit the cat in October in prep for its MOT.
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My inquisitive ( ok nosey ) side has to ask are you going to refit just for the MOT and then remove again ?

What difference has it made to the car apart from the stink :D .
 
A sports cat on the N20 is a great compromise..much better sound than a de-cat..passes MOT emission check by a factor of 2-4 times..as opposed to 200-400 times for a full cat…

Limited suppliers and price are the negatives..
 
What difference has it made to the car apart from the stink :D .

Hi 1536Z4,

Fitting a decat pipe allows the turbo to spin up faster. It’s also allows the remapping technician to remap the engine to a higher level. A stage 1 remap is software only and takes the engine to 260-270bhp whereas a stage 2 remap is based on using software and hardware such as decat pipes and bigger intercooler and can take the engine to 280+bhp. The decat pipe gives the engine a growl under power and lots of bangs on pops when in sports manual (mines an auto). I quite like the sound.

Yes it’s my intention to refit the decat after the MOT unless it proves to be an expensive option in which case I’ll have it remapped with the cat fitted.
 
Nictrix said:
I thought it was now difficult to remove the DPFs and pass an MOT as if there is ANY smoke coming out of the exhausts at all its a fail.
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The quote was from an MOT test trainer, so I guess he knows what he's talking about. As mentioned, there is a smoke test, but DPFs don't clear the smoke, jùst the particulates in it.
The tester can only look for the existence of a DPF, he will not remove undertrays and will have no way of knowing it has been tampered with if the method used is not visible.
 
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