Double-piston pop-off valve with external vent for Subaru Impreza 2000 Turbo 16v by ProtoXide.
Distinctive "laser effect" sound emitted on venting.
Designed to avoid all the issues that other pop-off valves cause on cars equipped with a mass airflow sensor, such as Subaru models.
Highly useful valve to prevent the dreaded pressure surge (water hammer), which is very harmful to the engine and throttle; it prevents surge during throttle lift-off.