DECAT Passing MOT Emissions Test

[wrxtom]

Hi, this forums been a good source of helpful advise and information since owning my Impreza, so today thought i'd share some of my recent findings regarding de-cat'ing certain sections of the exhaust system and if a newage WRX car would still pass a standard UK MOT emissions test.

My Impreza's an 05 WRX Blob, the engines basically stock, and with the only mod being a Hayward and Scott 2.5''  resonated rear centre section and back box ( retaining all 3 standard catalytic converters)  it made 269BHP when re-mapped at TDR in Warwick. Shortly after that it had its MOT and passed its emissions test as expected with ease.

After a while (and rather typically) i've become used to the power and in the new year will be looking to make a bit more, so it now has cooler plugs, HKS panel filter, walbro 255 fuel pump and most importantly a gutted/decatted stock up-pipe and a Japspeed decat down pipe, whilst retaining the standard centre CAT. (I also have 650cc injectors to fit but wont be doing this until the car is re-mapped again)

I popped into see my local MOT tester the other day as i was curious to see if the car would pass a UK MOT emissions test, or even be affected by having 2 out of 3 CATS  removed.

As can be seen from the photo below showing both results the emissions test shows to be basically un-affected by the removals, and passes with flying colours by just using the centre CAT. Thought this information might be of help to anyone looking to de-cat some of their exhaust, but curious if they'd still pass an MOT. Thanks for looking, Tom

[Tidgy]

Just find a friendly MOT centre and sack off the cat's completly.

 

As far as the injectors just sell them, they arn't needed, unless your planning on having the engine rebuilt with forged pistons etc.

[wrxtom]

Wasn't really looking for advice thanks, just posting my recent findings. 

[Scoobyghost]

Smells a bit fishy. With no catalytic converter there is no way a car will pass an emission test.

Were the garage aware of it being a decat?

Is it actually decat or are you using the term decat meaning non resonated?

[GeoffLeggy]

Different exhaust setup by mine gets by on the 1 dinky downpipe cat. 

[Assa1974]

On 22/12/2017 at 8:37 PM, Scoobyghost said:

Smells a bit fishy. With no catalytic converter there is no way a car will pass an emission test.

Were the garage aware of it being a decat?

Is it actually decat or are you using the term decat meaning non resonated?

The OP never said they'd totally decatted, though. They have removed 2 out of 3 cats. Obviously the remaining cat is perfectly adequate in terms of the MOT test. Technically running with no cat at all is an automatic MOT failure irrespective of engine emmissions.

[Scoobyghost]

The OP never said they'd totally decatted, though. They have removed 2 out of 3 cats. Obviously the remaining cat is perfectly adequate in terms of the MOT test. Technically running with no cat at all is an automatic MOT failure irrespective of engine emmissions.

A blob only has 2 catalytic converters commonly referred to as "cats". The 3rd box is simply a resonating box used to quieten down an exhaust. A lot of the time a resonator will be incorrectly identified as a "cat". Leaving that box on will not affect an emissions result. The op reads as having removed the up pipe and down pipe cat, leaving the car completely decat.

Obviously a car with absolutely no "cats" will always fail an emissions test.