Hi Adam,
If we take cat off and put pipe etc , what about MOT? Does this not get the inspector scratching his head :doh: only they are a right lot out here in Spain what with CO and the look at everything with tape measure in hand can't change anything here without permission off them or car maker .
If the EU type approval certification says that a cat is fitted and you remove it it should fail, it almost certainly will here in France. Technically the same applies to changing the intercooler, fitting a boost controller etc. For any of that stuff it should be submitted to the road transport authority (DRIRE in France) for approval or you will be uninsured