HV oil pumps tend to make better pressure @ low RPM with hot oil, the rotor of a HV pump is larger, moving more oil per revolution with the same relief spring pressure setting as a standard pump. Hi volume pumps also remove heat faster than a standard pump at the cost of consuming more HP to drive them. On a tight new engine a standard pump works fine, On a loose engine or a larger engine the Hi volume works best, providing the pan has the capasity for the flow.