This is a factory setup for chevy 261..was in 2 ton grain truck.. Ran in present configuration with present pcv valve.. I ordered another pcv valve (same part number) and it is identical with small orifice and nothing else.

At idle with high vacuum you would have a given flow through orifice just like normal pcv valve.. As throttle is opened and vacuum drops.. The flow would also drop... No vacuum leak as.. No vacuum. Sound correct? Seems like a workable system considering grain trucks were full throttle most of time

Doesnt matter too much .. My original question of whether it would work with a zenith carb off gmc 270... After thinking about it it shouldnt matter.. Im putting system in this weekend so ill post results later


Old Truck addict
1950 chevy 1 ton napco
1956 gmc 1 ton dually napco
1954 chevy 3/4 ton napco
1957 gmc civil defense napco panel