Perhaps we could get a mod to sticky this.

In doing some research on the elusive small block oil pump gasket, which has proved to be inconclusive. I think that topic has ended friendships and possibly marriages.

I found that there is a lot of confusion on oil pumps and oil pressure were high volume vs high pressure is concerned.

Part of the problem is the name doesn't necessarily tell the whole story. Both pumps may provide higher pressure depending on the situation. I know so far we are clear as the mud we like to play in, right?

First lets look at volume vs pressure. Volume is flow, its about how much liquid is being moved. Take a garden hose for example. If we have our hose with the water turned on all the way we have a lot of water coming out per minute. That is our volume the amount coming out per minute. however it has very low pressure. Now if we restrict the opening at the end of our hose with a nozzle we start to limit the volume of water coming out of the hose. When we start to limit the volume at the end of the hose we increase the water pressure. So as you can see volume and pressure are different but related.

Now we will look at the high pressure pump. A standard high pressure pump doesn't provide any more volume. It provides the same volume as a standard pump. The difference is that the bypass valve has a stiffer spring in it to allow a higher pressure before it opens. The bypass valve regulates the pressure in the system. The high pressure pump doesn't necessarily raise the oil pressure in the engine it just allows a higher maximum pressure to be achieved.

A high volume pump will provide more flow to the engine. Simply it can provide more flow. A standard high volume pump will not provide oil pressure higher than the stock specified pressure (give or take a little). The reason for this is the bypass valve will open at the same psi as the stock one. All of the additional flow provided by the pump, not needed to provide the engine with the specified oil pressure, will be returned to the pan through the bypass valve.

Now where it really starts to get confusing. The high volume high pressure pump. This is the same pump as the standard high volume pump but it has the same bypass valve as a high pressure pump. So now we have increased flow and a higher maximum pressure.

How does all of this translate to oil pressure in the engine. In a fresh engine with proper clearances, the high pressure pump will more than likely increase the oil pressure. A high volume pump will not increase the pressure as it will simply open the bypass valve and bleed off excessive pressure. The high volume high pressure pump will all most certainly increase the oil pressure, since it is providing more volume and the bypass opens at a higher psi.

In a worn engine or a high performance application with high clearances, things are a little different especially an engine experiencing low pressure with a an OEM pump.

A standard high pressure pump will have little to no effect on the oil pressure in this engine unless the OEM pump was defective. The reason being is that the pump will not provide enough volume to fill the gap in the bearings. It the flow isn't restricted and can easily escape the bearings the pressure won't get high enough to open the bypass valve, negating the need for the heavier spring.

A high volume pump in the same engine should provide a boost in oil pressure as it is moving more oil to fill the area between the bearing and crank/cam. If the pump can move enough oil, this will raise the pressure closer to the factory spec oil maximum oil pressure; possibly even reaching that spec. It won't exceed it since the standard pressure bypass valve will open at the same psi regardless of volume.

A high volume high pressure pump in a worn engine may or may not provide oil pressure higher than the maximum OEM spec. Depending on whether or not the pump can provide enough volume that the oil is restricted enough to provide the pressure.

As far as hardened oil pump drives and extra capacity pans, I can only provide what I've seen. I know my dad has put high volume pumps in every engine he has ever built, and it's been a few. When I brought up the hardened drive, he had never heard of such a thing on a Mopar. Also all of them were running stock pans. Never had one suck the sump dry. We did usually run a half to full quart over full but part of the was we used the longer filter that Ford uses instead of the short on Mopar uses. Granted these are not 8000 rpm motors mostly daily drivers or farm pickups.

I hope this helps you out in trying to choose an oil pump.