to clarify,
all turbo cars will have a DV (diverter valve or dump valve) as standard. or perhaps anther system that does the same.
most are designed so you can t hear then, and also at stock boost levels on lower power cars they would be difficult to hear.
if you have a dv that can run the other way around, this does not mean the air goes the other way. the air will travel in the same direction as originally, but will exit the dv from what was originally the inlet.
Some turn them around as it may sound different. perhaps some thing it is louder as it doesnt work as efficiently allowing the boost to build up slightly more before it operates. which isnt a good thing really.