Thanks for your help guys^^ Just got it done this afternoon in a garage near my hse for 40 pounds^^ Take about an hr or so... havent got a chance to test the result yet, coz i gota go out before they finish, and my bro. andrew (black 350z owner) pick up my z for me, and told me it pop a lot more now but not as loud as he thinks.
Also the OEM cat is SHITTTTTTT!!!! (sry, if u like it) It weight a ton compare to my new japspeed silent de-cat. Anyway, gettin my car to abbey tomorrow morning and get it re-map. Hope i can get a gud result ^^ But what sort of gain do u think i m gonna get? My z is a 53 UK version, with japspeed silent de-cat and y-pipe, amuse R1 titan exhaust, blitz induction kit (or u think i will get a better gain with JWT popcharger?), and a skunks 2 5/8'' spacer.