Purpose of precats

[Antti O]

Hi
I have been thinking what is the real purpose of front cat which is after exhaust manifold. My car has Akrapovic evolution exhaust system which deletes main cat from center part of the exhaust. What i found out, that car will pass emissions test even it does not have main cat at all. So what is the purpose of precats which are in the exhaust manifold. Or why there is main cat if front cats are enough..

 

[AaronJeff]

Ive always wondered this too! ... It might not be to pass an mot, it might possibly be to reduce the emissions enough to be in a lower tax bracket

 

[Foxspeed]

theres 2 of them because they treat and clean the exhaust gas of certain pollutants...

nox cat and hc/co cat most likely

why do they pass the test if removed - they are there to clean up the gases and do it over a period of time and when the engine ages so a good engine will give lower pollutants out but will most likely fail when the engine is operated outside of the mot test...

not only that but the law dictates the cats have to be fitted to meet emission standards iirc

 

[Antti O]

We will see if my car passes mot check in next summer. So foxspeed you say that maybe front cat is for hc/co and the main middle cat is for nox? In that emission test we have here in mot check i dont remember there was nox measured. Only O2, CO2 and HC.

 

[N0ddie]

Our old 200 passed UK MOT emissions with the Akrapovic evolution fitted. Passed with room to spare IIRC.