Charles,
First off the reason that they make it a point to in their ad that the Pontiac pump is high pressure (hp)and not high volume (hv) is for this reason. The after market makes high volume pumps for just about every common make and model engine with the exception of Pontiac. You may have noticed that in the ads for the Chevy and Ford engines they advertise high volume. They don't want you to think your getting a hv pump like everyone else is getting. There is no advantage to a hp pump over a factory Pontiac OEM pump. All hp means is that it has a stronger spring in the check valve and that's it. Volume is the amount of liquid that will be delivered in a specific period of time, like 10 gallons per minute (GPM). Another way to explain it is this. If you had a hydraulic cylinder that had a 10" piston and a 12" stroke. Lets say that the volume equated to 2.6 gallons and you pushed on the piston and it took you one minute to empty the cylinder that would be a delivery rate of 2.6 GPM. An automotive pump is a hydraulic pump and it has a specific volume it will deliver per revolution. The higher the RPM the more oil that will be displaced over a given period, i.e., GPM. This volume of oil per revolution is constant regardless of pressure. Pressure is determined by resistance pushing against the oil flow. The maximum pressure in the system is determined by either the pressure relief valve (check valve) or the level of resistance to the flow. Lets say that you have an old engine and the bearing clearances are quite large and an excessive amount of oil is leaking past the bearings, in this case the oil pump volume may not be adequate to build enough pressure to reach maximum pressure. In this case there is so much leakage that none of the oil is going past the pressure relief valve. In this case a higher pressure oil pump would NOT increase the pressure no matter what. Now if you installed a higher volume oil pump and the volume or oil supply (GPM) was increased enough additional volume could create enough resistance to exceed the pressure setting of the pressure relief valve then started to by pass oil then you could reach your maximum oil pressure determined by the relief valve. The Pontiac engineers designed what is called a gear pump for their oil pumps. No one sells a higher than stock oil pump (there is one exception and it is made by Titan and it is very expensive). The gear pump has a chamber and two gears rotating in opposite directions. The only way to increase volume is to spin the gears faster or make a larger chamber and larger gears so more oil will be displaced per each revolution. Volume and pressure are related. Let's look at another example, Lets say that your pressure relief valve was set to by pass oil at 60 psi (60 lb. pump). In this example if your clearances were large enough that the oil pump did not provide enough volume to by pass the relief valve until the engine reached 6,500 RPM and you were shifting your car at 5,500 RPM then you would never reach 60 psi. In this example lets say that at 5,500 RPM your pressure only reached 50 psi. If you installed an 80 lb pump your pressure would still be 50 psi. Now if you installed a higher volume pump that had a volume capacity capable of exceeding the supply needed at 5,500 RPM then this would increase your pressure.
Tim Corcoran
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Tim Corcoran
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