Quote:

Hi volume pumps more oil.



Yes. and more oil through the same clearance means more pressure. That's why a HV pump improves pressure in old engines.

As mentioned, the spring is what decides the pressure. but ONLY if the pump is capable of moving enough oil to reach the spring pressure.

From my own experience, a HV pump is nothing but a waste on a fresh motor. I had a the relief stick on std pump once. It moved enough oil at just off idle, that it blew the filter up like a balloon. All this, on a motor with .003 main clearance.

I reringed a 400 a few years back, and had teh same issues as the original poster while using an hv pump. Switched to standard, no problems since.