BigBob, I did put a thread out on this subject quite a while back. You do need the cat for the Mot, UNLESS you know the tester very well...Apparently, if u copper grease it nice enuff, u can take the cat off and on easily at the Mot time...Not sure if thats correct in regards to the Copper grease..I am thinkin of taking my Cat off and upgrading the manifold.. My mate has done it, u can notice the difference..