# Sport cat exhaust emissions test UK mot



## C00P5TT5 (Jul 10, 2016)

Just sharing my experience with you so you are well informed.

Put a turbo back scorpion exhaust system with sports cat on my car last year and it passed the mot.... Granted it took a few attempts.

This year the same guy failed it.

Now before I go on I would like to mention that I phoned scorpion UK and asked would it pass and they said yes.

So I asked my mot tester, why did it pass last year but not now, knowing I have no other issues with the car. He said they are getting more strict with the emissions.

Not sure if was a case of the cat not getting hot enough, or him being by the book. But it would seem to me that sport cats are struggling to pass the test....... Wish I had gone decat now!


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## Enky08 (Dec 7, 2018)

Same reason I went decat this time as APR sports cat on my gti wouldn't pass at all last year. Like not even close


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## Barr_end (Oct 19, 2016)

Funnily enough, I had the opposite with my Milltek sports cat this year, which is about 4 years old!
Struggled to pass, too 2-3 minutes of revving in the workshop to get it hot enough.
This year only took about 45 seconds to a minute.
100% advice giving it some death and driving it in a low gear at high revs on the way to the centre and try making them get it straight in and on the emissions tester, so there is some heat in the cat


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## Danny1 (Sep 2, 2010)

My scorpion cat flew through on the RS last month.


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## p1tse (Sep 20, 2004)

Enky08 said:


> Same reason I went decat this time as APR sports cat on my gti wouldn't pass at all last year. Like not even close


How do you get a decat to pass
Friendly mot or swap over with a cat?


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## pdk42 (Apr 23, 2018)

Contrary post I know, but... why do any of this exhaust tinkering at all? From what I can see the performance gains are modest at best and of course you're increasing both noise and exhaust fume pollution. If enough people did this sort of mod then the impact on public health would be significant.


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## Danny1 (Sep 2, 2010)

pdk42 said:


> Contrary post I know, but... why do any of this exhaust tinkering at all? From what I can see the performance gains are modest at best and of course you're increasing both noise and exhaust fume pollution. If enough people did this sort of mod then the impact on public health would be significant.


Its alot more power on certain engines and like you say most people prefer a nice sounding exhaust. On pollution ROFL i hope your trolling and if so gratz because im going to reply anyway, maybe you could sell your car and buy a push bike to make up for anymore pollution Im making :lol:


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## FNChaos (Nov 30, 2016)

Modern catalytic converters are very efficient and you will see little to no gain on an unmodified vehicle by going catless. (Might have made a difference a decade or two ago but that's no longer true)
IMHO you won't see enough improvement even on highly modified motors to justify the hassle come inspection time.

Now there is a reason to replace your original factory cat with an aftermarket sport cat if you modify your motor and that has nothing to do with increased power but rather the ability to handle more heat before melting.


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## pdk42 (Apr 23, 2018)

Danny1 said:


> pdk42 said:
> 
> 
> > Contrary post I know, but... why do any of this exhaust tinkering at all? From what I can see the performance gains are modest at best and of course you're increasing both noise and exhaust fume pollution. If enough people did this sort of mod then the impact on public health would be significant.
> ...


 Whatever. I can see that you're clearly not seeing my point.


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## Enky08 (Dec 7, 2018)

On my mk7 gti I dyno'd at 316hp with just software and same dyno only adding a "sports cat" downpipe it made 347hp so there's 30hp on a downpipe that failed emissions test no matter what we tried. So may aswell have been decat. Nearly 10 percent gains is worth it to me! And £850 for sports cat which failed, £350 for decat, do the maths.

On this platform there is basically no difference between stage 1 and 2 but I wanted to try it to see what the noise was like, it's alot more raw, less muffled.

As for emissions, you are barking up the wrong tree. All these manufacturers pushing "clean" diesels and flooding the world with them has polluted the cities more than the small percentage of modified cars running decats ever will. Just my 2 pence


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## Barmybob (Nov 4, 2015)

Enky08 said:


> All these manufacturers pushing "clean" diesels and flooding the world with them has polluted the cities more than the small percentage of modified cars running decats ever will. Just my 2 pence


This topic was started with regard CAT emissions on petrol engines. One of the main things a CAT does is remove NOX (NO & NO2) from the exhaust of a petrol car. So to remove a CAT you are, in effect, turning your car into a NOX producing "Dirty Diesel" :roll:

The current Diesel hate is with regard these NO2 (NOX) emissions. Diesel became popular because it significantly reduced CO2, and when fitted with a DPF also significantly reduced the well known Diesel particulate matter too.

The development of GDI / TFSI motors sought to reduce CO2 in petrol cars. The CAT was already dealing with the NOX so CO2 reduction, and greater efficiency, were good goals. The only bad thing was that despite knowing about increased and harmful particulates, the cars were never fitted with particulate filters!

So, A TFSI motor, without a CAT & without a particulate filter would indeed be a very "Dirty Petrol"


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## Enky08 (Dec 7, 2018)

I know, that's my point entirely.

Worrying about a few people who have modified their cars which produce nasty NOX while manufacturers have been pumping out millions of them claiming they are clean. What's having the real impact? How many decat cars are there compared to diesels?


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## gutsu (Mar 5, 2016)

Please forgive me for being stupid but if a sports cat fails an MOT how will a decat pass?


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## FNChaos (Nov 30, 2016)

gutsu said:


> Please forgive me for being stupid but if a sports cat fails an MOT how will a decat pass?


It won't.

The point being made is, if a modified exhaust fails MOT with a sport cat installed, might as well have saved the money spent on the cat since a failure is a failure.

That being said, many people do successfully pass MOT with a sport cat whereas you are guaranteed to fail if you go catless.


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## FNChaos (Nov 30, 2016)

I realize most people understand what a 'Sport cat' (catalytic converter) is, but for the benefit of lurkers and auto-mechanic neophytes here are a couple of pictures:

The first pic shows a typical sport cat (can of WD40 is for scale). A catless exhaust would simply replace this component with a piece of straight tubing.










Picture 2 shows the inside of a sport cat. OEM cats are usually made up of a honeycombed ceramic block. In the case of a sport cat, the core is made up of corrugated metal foil wound around itself. 
If held up to the light you can almost see right through the core (demonstrating how nonrestrictive they are).


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## cryptorennie20 (2 mo ago)

C00P5TT5 said:


> Just sharing my experience with you so you are well informed.
> 
> Put a turbo back scorpion exhaust system with sports cat on my car last year and it passed the mot.... Granted it took a few attempts.
> 
> ...


decats are also illegal and you won’t pass your MOT


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## Barr_end (Oct 19, 2016)

cryptorennie20 said:


> decats are also illegal and you won’t pass your MOT


Was it really worth the 3.5 year old thread revival just to post this?


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## ab54666 (Nov 18, 2019)

Took mine for an MOT today, I have the Scorpion Sports CAT onto the standard exhaust (TTS).

Gave it plenty of beans on the way so it was nice and hot and had no issues passing.

CO (fast idle) which has a maximum of 0.2 came in at 0.15, natural idle which has a maximum of 0.3 came in at 0.13
HC which has a maximum of 200 came in at 41


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