if you want it to properally pop and bang then you need an after market exhaust, i wanted to keep mine quiet as i do alout of miles and sometimes get back from work at 4am and dont think my neighbours would be pleased if they heard me every week lol

it will pop more with a decat though than a cat

the power increase is noticeable, its more tourque than hp the 4-2-1 is for torque the 4-1 is for hp i think

alex