I had some twin side pipes fitted to my S1 last year. They look & sound great, very much like a C63 AMG merc, thunderous at revs and yet restrained when below 2000 rpm when cruising. Fitted by Hayward and Scott. Interesting was the incredible weight of the old silencers when removed (2 per side) , which I have kept. 40 to 50 kg per side, so some considerable weight saving, but I don't know how much the new single silencers per side weigh. My estimate is an overall 50 to 60 kg saving