Hi Greg, before we had air pollution controlled cars they had road draft vent that went from the oil cap down toward the road an angle cut pipe using the forward movement of the car to create a vacuum past he pipe and lower the crank case pressure in the engine block. some time in the late 60’s crank case vents went to the air cleaners the be burnt and to lower crank case pressure at the same time. different from the PVC vent that goes to a port under the carburetor check the under or side of your air cleaner for 1/2 inch [about] male pipe end . good luck Dan