HKS SSQV blow-off valve
When the throttle body closes, compressed air is blocked and bounces back to the turbo. To prevent this returning air from forcing its way through the turbo's compressor, a blow-off valve can be installed. This one-way valve vents the compressed air to atmosphere (or recirculates it back into the intake) and can help prolong the life of the turbo as well as reduce turbo lag.
Due to the pull-type valve in the HKS Super Sequential Valve (SSQV), it can't leak under boost pressure and is regarded one of the best since years.
How to install a blow-off valve (BOV)
Modifications - Engine