my plumb-back is just as loud, if not louder, than alot of Atmo BOV's i've heard... (assuming you have a Pod Filter as well)
it's a GReddy Type S.
the stock BOV is also quite loud, and works just as good... can pick them up for around $30 or less, so just pick one up, sell the atmo bov, and you'll have a car that's running better, will still sound tough, and you'll make money from selling the atmo one