Exhaust System

[brainbug007]

I'm starting to look into how I'm going to setup my exhaust system and any advice would be great I'm running a 1.8 cvh on bike carbs with a rs turbo exhaust manifold so far. The kind of thing I'd like to know is what sort of pipe diameter do I want going from the manifold to the silencer (as doesn't this affect flow rate which affects bhp?) and what sort of silencer is a good but reasonably priced? I wasn't planning on going for anything posh like stainless or chrome as I'd need to be able to weld it all together I guess with my mig and my welds won't be that pretty.. I've seen some slip on things though and would these just need clamping instead of welding?