My cousin had a cobra exhaust on his 350x and it was loud as hell, sounded like ****, started to fall apart and when he changed pipes he noticed a big defference in power. Basically cobra exhausts suck and I think that it would be a complete waste of your money.
i have one.. but i took it off only b/c it was just to laoud.................ut it deffinatly give your power in the mid range.. it does basically nothing in the low and really high end.....
also remmeber its they are really noisy from my experiance