I'm thinking about making an underslung exhaust/muffler. The actual fabrication I can do, but I've no idea about dimensions/flow rate/volume etc. Is it a matter of trial and error, or is there a hard and fast rule to apply? Or would I be better off modifying something that already exists?
I haven't got the bike yet, but I'm trying to get a plan together in my head for when I do. It will be an IL4 1000cc (never owned a 4cyl. Ridden a couple, but I've always had twins)