every single move altering the original parts with non approved (or not yet approved) parts have to get permission from Bapak JPJ and Mak Puspakom. If the parts are already approved (have certificate from JPJ) then only can use.
Like while I was at the States, most parts have to be certified 50 States Legal by their authority. Even Apex'i gadgets have these certificates!!!
Reddice :
I spent around 300 for the catback and another RM100 for the fibre and tailpipes, and yes the tailpipe is solid 2" stainless steel pipe, no exhaust tips... it's much leaner (leper) than the ori GTi box and it's just nice, not so noisy, and I still manage to reach standard top speed of 1.6 SOHC and better pickup. I'm not an exhaust pro, and little bit lost about ur 'sometimes' part because that tends to be normal, with our feeling, when it's just actually the same... if you know how to control throttle, can get good response from the SOHC, but if you buta buta floor it, then u'll only get bassy sound but no go. just my 2 cents... but DOHC engines are much responsive to floored throttle..