Is it illegal to add a catalytic converter?

[Tillerz]

Hi guys,

So searched the forums, couldn't find anything on adding a catalytic converter.

My question has multiple parts:

1) is it illegal to add a catalytic converter?
2) also does positioning matter, say adding one cat before first O2 sensor in addition to the factory one which comes between O2 sensors.
3) this kinda is the same as second part, adding multiple cat in replacement of one cat. For example, turbo'd a car, but wanted to stay environmentally friendly, (lets not worry about performance/back pressure issues as this is just me stating an example), and i added 2 cats in the place where there were one factory to help minimize emissions released into the air, is this illegal?

Thanks

[baggdis300]

lol why would it be illegal?

my car has 3 cats stock.

its only illegal to REMOVE cats

[Soundy]

It may not be illegal, but I don't think it's a good idea, especially if you have multiple O2 sensors. Putting a cat ahead of an O2 sensor that doesn't normally have a cat ahead of it will affect its operation and could cause even bigger issues with performance and emissions.

[some_punk]

It shouldn't affect performance if you put it after the second O2 sensor. cats aren't really that restrictive. In fact on some cars, the cats have the material inside positioned in such a way that it helps with the air flow.

[Soundy]

Put it AFTER ALL the O2 sensors, no, it should have a direct effect on performance.

Still... I don't see the point, especially with newer cars - here are so many sensors monitoring everything that goes in, on, and out, with the computer constantly managing every part of the combustion process, that emissions are negligible to begin with.