I have some experience in the design and operation of gear pumps used to pump molten plastic. They are similar in design to an
oil pump. FYI a small amount of the molten plastic flows through the bearings as a lubricant. Pump range is size from a few hundred lb/hr to several hundred thousands of lb/hr.
Torque is proportional and linear to the pressure. So, if you double the pressure you will double the torque required to turn the pump. The point is that increasing either the pressure or the flow will put more load on the distributor gear.
Pressure is the result of friction resisting flow. An orifice plate is often used to measure flow, by measuring the delta pressure across the plate (restriction). Flow is measured by taking the square root of the delta pressure. Therefore as flow increases, the pressure increases by the square of the flow. P = mF^2. The point being that a small increase in flow will result in a large increase in pressure.
No pump is 100% efficient, if the exit pressure is higher than the inlet pressure (delta pressure). Efficiency drops off as a factor of the delta pressure squared. So, as the pressure increases the efficiency of the pump and thus the flow will drop off. This all depends on the clearances in the pump. The point is don’t forget to blue print the pump.
Engine
oil pumps have a pressure relief valve that opens, lets say at 70 psi. So no matter how much volume of
oil the pump puts out, the pressure to the engine is limited to 70 psi. At 70 psi a certain volume of oil will flow to the engine, for a given temp and viscosity oil. If the pump is putting out twice this volume of oil then half is flowing to the engine and the other half is bypassing out the relief valve. Therefore half of the hp used to pump oil is wasted.
A high volume pump, with the same relief valve setting as a normal pump, is only going to supply more volume to the engine at lower rpm, when the pressure is lower than the relief valve. Once the relief valve is open the extra oil is dumped out the relief valve. It does nothing for the bearings, and worse it waists hp.
Going to a higher relief valve setting (spring) on a stock pump makes the most sense to me. However all the bearing and other clearances need to be, on average, near the middle of the specs. A loose engine is going to need more volume to build the same pressure.
I have never been a big fan of high volume pumps. I’m sure there are times in all out racing that it may be useful in certain engines. Most Ford pushrod engines suffer from a poor designed oil system, and a high volume pump will do little to solve that.