Whats the deal with it, as I know turbos, but not n/a at all.

Was talking to someone with a 968 yesterday and he was talking about doing a few mods (they already 240bhp from a 3litre 16v 4cyl n/a) and though he was on about some posh Porker tuners that charge a fortune, I didnt even know what sort of exhaust size would be any good TBH.

If all the boxes were straight thru, so no restriction there, how do you work out size (obviously its not an exact thing, lots of variables, but roughly)?
Is just it on bhp? Or capacity too?

What would be a good size for a 240bhp 3litre?

Teach me!