Is it worth de-cat the downpipe on a uk 99 impreza, are the gains worth the trouble of putting cat back on for the mot. If so is it a easy job to do and what are the best ones to buy, and what happens to the sensor thats in the downpipe.
My car has the middle cat off and a performance back box, apart from that its standard and i am getting the power bug but on a budget lol

 

On its own its not worth it. With a remap then the gains are more inviting.

the downpipe cat is much more restrictive than the cat in the centre pipe so you can (with a remap) exploit that.

Come mot time, if you put the centre cat back on should get it through emissions. Much easier than replacing the downpipe.

Our just get a sport cat downpipe and not worry about emissions. Obviously more restrictive than on open free flowing decat but less hassle.

 

The lambda sensor goes in the the same place on the new downpipe. most decent ones come with a boss already welded in.