I had a ported Dbilas manifold, custom 2.5" down pipe with 200 cpi cat, remus silenced centre section de restricted and remus twin 3" round back box also derestricted on my Vectra B. sounded good, low down burble, shouted when giving it the beans but cruised nice and sensible. tried straight through centre pipe but was ridiculously loud and gave no power gain over silenced centre section so removed it after 5 days! still got the remus sat in the shed and the race tube.