I have a SSQV HKS bov on my ZXT, it's the loud high pitch sound. I don't really like it, so I changed the fin insert to a purple one, and it made the pitch lower and deeper... more pshhh than peeef. The HKS can be plumbed back, you have to buy a kit from HKS to get it plumbed back, but it's expensive for a basic kit, ~58 bucks the last time I checked. Anyway, if you want to vent your blowoff to the atomsphere without the hesitating/super rich a/f for a few seconds thing, see if you can get ahold of an HKS EIDS unit, they sell for about 100 bucks in Japan and allow you to vent your blowoff without the backlash of problems.
John