I left my air intake and A1 as standard although I understand the addition of K&N filters does make a difference to performance (I kept as stock so no risk to warranty). As for A1 I like popping and the odd backfire so left well alone. Use your regulator to change sound also - lower gives you more snack crackle and pop! But careful not too low as it dies on you as I found out in the centre of Dijon next to some HD boys. Not my finest moment! Btw if you take off the A1 you need to bypass the O2 sensors on EFI (I think).
