So, a catless downpipe could have a visible odor, because the exhaust emissions aren’t noticeably transformed. To paraphrase, they’re not being cleaned. For that purpose and as it will help the ecosystem, many people pick the catted Model of a downpipe. The after-market place downpipe is tested to improve performance. https://arthurafkos.eveowiki.com/876807/not_known_factual_statements_about_downpipes_rs6_c8