That's what they said. I interpret it like this : the bypass channel in a typical sbc oil pump enters the inlet channel in a 90° fashion. Due to it being pressurized I think it will hit het opposite wall causing it to go into 2 directions, 1 part in the direction of the pump gears and the other part in the direction of the pickup disturbing the inlet stream. I must say that I witnessed the results from something similar but in a different area. Someone was filling a gasoline tank from a pipe that entered the main fill pipe at an angle of 90°. The flow of the gasoline went in the 2 directions, with one half exiting the open part above the T-fitting, the other half went into the tank below the T-fitting. Schumann indicated that this lowered the inlet pressure, causing cavitation. Of course this could be totally unfounded. I'm not an engineer, so I do not have the necessary capability to verify this. I agree about the possible air entrainment problem, but I have to assume it would be as big with an internal bypass ? Both systems work similar with the one exeption that the external relief valve would exit in the pan below the oil level. I do not see how air could get in there unless the pump was already sucking air.