Removal of the catalytic convertor...

[mystik]

Went and got my California smog check for my upcoming yearly car registration and after it was all over and done with, I wanted the cat gone. Why? I wanted a louder exhaust system, basically. As for performance, a lot of people were saying that the sensors will get all messed up and that it'll pretty much ruin the car if I drove without a convertor. I'm not too concerned about going faster and I'm sure removing the cat will not hinder my performance. But... What do ya'll think?

Leave the catalytic convertor or have a straight pipe setup? What are your views and opinions on removing the convertor?

 

[ksher]

In UK, removal of catalytic convertor will fail the emission test.

 

[hotdog3147]

Just leave it on, over this side of the pond, de-catting a car is a mod done by idiots in over tuned cars. The 3.0i engine sounds good enough without making it sound like a rally car, which would wreck the whole image of the car.

 

[GAZA62]

As above leave well alone its a Z4 not a Hot Hatch with a nasty body kit :thumbsdown:

 

[sammyz]

If you want a louder exhaust note go for a new back box, there are some good ones on the market which will give a louder, deeper sound without sounding too chav.

 

[Shipkiller]

Removing your CAT will not hurt the engine.

BUT

You will get a SES light, since the DME will see no difference in O2 sensor inputs between the front (pre-cat) sensors and the rear (post-cat) sensors.
The only way to remove this 'reliably' is with a DME software change. I have seen some other ways of overcoming this over on the E46 forum, mainly used for installing headers which have no cats, some work, some are hit or miss, but a software change is the preferred method... and expensive.

If you really want to remove the cat and go through all that trouble, you ought to get a set of headers. You will be louder, have more power and better fuel economy.

How do you 'over tune' a car?

 

[Adam D]

In UK, removal of catalytic convertor will fail the emission test.

Unlikely on a modern car with multiple catylitic convertors, my last car would pass with only the pre cat installed and the main cat removed. Even with no cats installed it was a borderline fail and that was on a 16v turbo engine from japan deigned in 1994 so hardly cutting edge.

The problem with the Z4 is I believe the o2 sensors are connected into the cat's upstream and downstream so your bypass pipe would need to accomodate them.