Librands is the only company, as far as I know, that offered an upgraded system off the shelf. Having said that my S1 has a big bore system fitted by a previous owner, a non Librands of unknown origin!
1969 4/4 1995 plus 8 1996 Plus 4 4seater 2002 Aero S1 2013 M3W 2014 Plus 8
