Okay I know I’m in for some ridicule here, and I do apologise in advance,
I’ve read of people saying catback exhaust being a good thing to do. What is it, is it the removing of the catalythic convertor, so producing a straight through exhaust and a potential MoT failure 
I’m not taking the pee, I want to know, please any help
When that expression is used, it refers to changing all the pipework and boxes after the cat, you can remove the cat on the earlier 1.6 cars and still pass the MOT [unless a canny tester spots that one should have been fitted
] But on later cars they wont pass the emissions test
Thank you once again Geoff, so everything back over from the cat to the tail pipe.
there are also so called ‘sports cats’ available which have a much lower back pressure and hence provide better gasflow and still pass the MOT, these cost around 350 pounds
super diagram