I know this is probably a umb question but im sure someone can answer it for me easily ...

I have a full afterburner vortex decat system to fit to my classic, say i decided to only fit the backbox and the centre pipe, leaving out the one that connects down at the turbo end, would this mean my car would still fail an emissions test?

 

No it will most likely pass, The cat (downpipe) you are leaving on is the main cat.

Most cars pass with just the centre cat in place (With a De-Cat Downpipe) and that isn't as effective as the downpipe cat.

Craig

 

sooo id be better off fitting the bbox leaving the centre cat and fitting the last pipe that connects to the turbo end? and would this way still pass an mot?

 

No i think you have miss understood.

Fit the center pipe and backbox and you will be fine

Craig

 

ahh rite, i get you, so the decat centre section is the middle pipe, and the decat down pipe is the one that connects at the turbo end? the latter being the one that counts when it comes to passing an emissions test...

sorry, ive just never looked at a full exhaust system in my life untill I bought this one for the impreza

 

For clarity it goes Turbo -> Downpipe -> Centre section -> Backbox. In classics like the P1 there is only a catalyst in the Downpipe as the centre section is only a resonator ( i.e. no cat just some baffling to change the sound) and the backbox is just that - a backbox. Other classics have an additional cat in the centre section but, as said above, if you leave the downpipe as it is you can do anything you like to the rest of the pipe and still pass the MOT.

Alternatively, you can buy a sports cat downpipe which is high flow, sounds like a decat and still passes the MOT - expensive though.

Finally, should you go for the full decat there are allegedly garages that will replace your centre section with a catted pipe for the test and then change back again afterwards. For about £70 a time, allegedly...

 

Brill! Thats exactly the explanation I needed, mucho appreciated!

Cheers guys