No matter what blow off valve you use, you need to recirculate the air to a point downstream of the MAF. The plastic Bosch style blow off works fine to 14lbs or so (I've personally seen them hold 18 lbs, just not for long) I want to say they are only rated to 12 lbs. Once you exceed the rating of the plastic bypass you should consider the Mondo bypass http://www.vortechsuperchargers.com/page.php?id=30024 I can honestly say that there is no noticeable difference in the sound from one valve to the next, function over form on this one