Try searching on ebay or google for neoprene ducting. It's available in lots of sizes but I'll be honest I dont think it's money well spent! You wont feel the difference at all, normally what happens is the ducting gets wet and the wire on the inside of the ducting goes rusty and just makes a mess to be honest!
^^^It makes a great noise mate.
Wish i could hear mine over my exhaust it used to love that sound
says on that post that you lose power. is this true? could do with a play tomoro
It sounded 100 times better from the outisde when you went up my street!!