I drilled some holes in the air filter box at the weekend using Jackals example as a template.
Very easy to do - even for me - and sounds great. Slightly louder on the motorway but only really when accelerating and not too intrusive. The sound on startup is super!
It's sound ace doesn't it? Mine has the original motor sound box on it from new (with the holes) which I believe was included in the lowered chassis option the buyer ticked.