I have a blow off valve, and I love it! Mine is recirculating, not atmospheric venting, so it's more muffled and sounds more like a PTSSSSSHHH than Jeff's WUUKKKTSHHHHHHHH!!!!! but it's PHAT yo!
Of course, then again... it's on my turbo Supra...
PS--> SolaraBlue, a BOV is not necessarily an aftermarket part. Some turbo/supercharged vehicles rely solely on a wastegate, but most (mid-80s and beyond) charged vehicles also come with recirculating blow-off valves (also known as dump, diverter, pop-off, bypass or anti-surge valves). Atmospheric venting BOVs are generally after-market, and are actually illegal for street use in several states. While the waste gate alleviates built-up pressure by allowing exhaust gasses to bypass the turbo side (and thus preventing the turbo from blowing itself up from continuously building pressure with no release), the blow-off valve dumps excess air from the intake side in order to alleviate harmful back-pressure from the compressor (known as "compressor surge", or sometimes incorrectly referred to as "wastegate chatter"). So it serves a very serious and practical purpose in the turbo system schematic.
