Ok, I've posted this on the engineers' forum, as it's an engineeringish type thing. However, not many peeps go there... So I thought I'd post a link on here in case there are any exhaust experts hangin' around. This is where to go: http://www.screwfix.com/talk/thread.jspa?threadID=66491 But, if you are a twit, or have ever been called a twit on this forum, please don't go there. Unless, of course, you are also an exhaust expert, in whcich case I'm very sorry if I called you a 'twit', even if you are one, which you probably are not.