Some further interesting information for debate. This explanation seems to make some sense (well to me at least!):
BYPASS OIL RECIRCULATION
Some pump manufacturers like to claim that recirculating the bypassed oil back to the inlet of the pressure pump causes the oil temperature to increase. Well, technically that is true. The problem is that the temperature increase due to recirculation is so small that it is difficult to measure accurately.
Those manufacturers who criticize recirculation claim their products are superior because, instead of recirculating the bypass oil back into the pressure pump inlet, they pump it back to the oil tank (or to the sump).
HOWEVER, sending the bypassed oil back to the tank (or the sump) creates an even bigger problem: The output of the pump at high RPM can be 30 GPM or more, while the engine requires only 8 - 12 GPM. That means that the pump will be bypassing at least 18 GPM through the relief valve to maintain the set oil pressure. If the bypass oil does not recirculate to the pump inlet, then the full pump volume (30 GPM or more) must flow from the tank to the pump inlet through the dash-12 inlet line, with only atmospheric pressure (at best) to move it. The reality is that it can't be done without reducing the inlet pressure below the vapor-pressure of the oil, causing pump cavitation, line collapse, aerated lube oil, and all the engine problems that follow those problems.
NRC pumps provide optimal pumping efficiency by recirculating the bypassed oil back to the inlet side of the pump.
http://nutterracingengines.com/racing_o ... pumps.htmlJust conjecture but the rear bowl sump used in the Escorts etc. and hence the longer oil pickup tube probably hastened the design change in 1973 as this pickup would have been more susceptible to oil aeration under high flow conditions