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I agree with you that the pump is a fixed displacement and oil is a non-compressible fluid, and therefore what goes into it must come out, but the bypass has a part to play in this. Since the volumetric flow rate equals pump displacement x RPM, then at some point this flow rate exceeds the capability of the restrictions of the oil system and pressure will build within it. When the pressure exceeds the bypass pressure setting, the additional volume will flow from the high pressure outlet to the low pressure inlet to be recycled internally. If the pump and/or block’s oil system are ported to reduce the frictional restrictions, the final point of exit for the system (bearings) will see a higher pressure and therefore flow, and less volume will be bypassed within the pump. Mitch shouldn't need to build a standalone test stand to measure the volumetric flowrate of a pump - the simplest method would be to measure the pressures directly at the pump outlet and at the end of the oil galley at the front of the engine block. If all else remains equal (temp, RPM, oil type and viscosity), he should be able to measure a lower difference of pressure between these points for his ported pump vs. a stock one to prove the porting makes them more efficient. I believe the oil pump is a small part in the entire system so it may be difficult to measure the dP with ordinary gauges, but there should be a difference between the two. The newfound oil system efficiency could be taken advantage of by reducing the pump displacement to maintain the same volume of oil at the bearings as original and reduce the amount of work absorbed by the pump which directly translates to more power to the wheels… now we’re talking. It wouldn’t be all that hard to do this to a VG oil pump... but without testing, it would be an uneducated crapshoot.
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