BOV boost pressure relief valve AMAZING SOUND EFFECT !!! It protects your turbo !!! The standard DV valve forces the air into the circulation, while the Blow Off valve - the atmospheric valve lets the air out, which protects your turbo, and at the same time produces an amazing sound effect - characteristic PSSSSSTT !!!! High quality. Dimensions: Inner diameter of the inlet (plunger): 47mm. BOV boost pressure relief valve AWESOME SOUND EFFECT !!! Protects your turbo !!! Serial DV valve forces the air into the circulation, while the Blow Off valve - the atmospheric valve lets the air out, which protects Your turbo, and by the way it produces an amazing sound effect - characteristic PSSSSSTT !!!! High quality of workmanship Dimensions: Inner diameter of the inlet (plunger): 47mm.