A GReddy blow-off valve releases pressure between shifts and when acceleration is cut short. When the throttle plate is closed pressurized air back-tracks from the plate and heads toward the compressor wheel in the turbo. If the charge air were to impact the blades of the compressor (which are spinning in the opposite direction) undue wear of the thrust bearings in the turbo can be experienced. The blow-off valve avoids the situation by venting the air prior to impact.