Herb,
These series of engines are full flow filtered. But at startup, with thick oil viscousity, there is a bypass that can and will open. This will allow unfiltered oil to bypass the filter. GM put this in so that when dummy's did not change their oil and the filter became plugged, the motor would still have oil pressure.
I plug the front oil spout to keep more oil for the crank/ rods. Later Gm engines did not use this feature. Plenty of oil flying around down there. Tom
