-so youve removed the dump valve!! where's the compressed air going now??---------i think you need to go read the principles regarding turbo's-
a dump valve is a safety valve much the same for any instalation regarding compressed air/water etc-etc.it releases pressure at a given point-very basic science!! you dont have to have the -HISS- of expelled air!!! recirculating does the job but i suspect you like to hear something to impress your mates. or to make you feel better in your car! so hows that reflect on your engine then!!!-