So correct me if I'm wrong, a standard STI (05MY) has 3 cats, once PPP is fitted it has 2 left? I've been looking on the hayward&scott website and they offer a straight through centre section (which replaces the resonator) and a 2nd/3rd cat pipe which fits on to the centre section. If I replaced these 2 pipes would I then only have 1 cat left and would this affect the ECU on the PPP and come MOT time would this be a problem? Thanks for your time and help. [*-)]