Huffer on huffer off ,is real easy for air to get thru.Basically a pipe,since said huffer is not gunna sit on top of intake,none of the oem style on off huffers sit on the intake,thats for the movies,the real ones are crank driven.I am not sure of the correct name of this valve is ,but heres how it works. You have a 4 inch pipe with a spring operated door{diverter} which opens under low pressure{no boost}apply the boost and the pressure in the pipe forces the trap door closed which seals the system and you are boosted,cut the boost trap door opens allowing fresh air thru the trap door into the carb.with the boost off there is no draw thru the huffer to worry about.picture a drain trap and a cross over pipe on the top .the top is where fresh air goes in unboosted.hit the boost and the top pipe is sealed via the trap door and then the huffer sucks the air thru the bottom of the the drain{instead of the top} around to the same spot only thru the huffer this time