its there to release the extra air created from the turbo when u ease off the throttle, so that ur turbo doesnt spike, so that ur turbo or engine dont get damaged, thus helping performance and is in no way a rice accessory (unless u dont have a turbo or sumthin lol, how does that work?)

 

ok here's the deal not you don't have to use a blowoff valve, you can use a bypass valve instead. how this operates is that it basically recirculates the air instead of dumping it (blowoff), it can prevent the car from running rich , which blowoffs can and have caused. but it never happened that much on fd i think. That's what it basically does.

 

is the sound from the bypass recirculating air still noticable?