Hi K Weng bro. myvi 1.3 (M) driver here(yit). currently using 4-1 ext & 1 exhaust with 2 tail and planned to change to 4-2-1 ext. how the different of single exhaust & twin exhaust system? prefer not too noisy but with some bass sound... btw, i am planning to go for open pod system. can quote me your best price.