Fishmen,
There is a limit to the amount of oil that can drawn through the pump up. When that limit is reached, it pulls air. Bearings do not like air...
Here is a quote from the old Mopar Perf book by Mopar man Larry Atherton on the s/b pump:
'Bob Tarozzi determined during his bench testing of various Chr oil pumps that the major restriction to their efficiency was the limited cross sectional area of the p/up tubes. Especially when the tall Hemi rotor has been installed, the pump is capable of pumping more oil than the p/up can draw out of the pan. Therefore, he recommends a larger diameter p/up tubes in all instances'. This is the SB pump.
BB pump:
'The B pump supplies more than twice the oil necessary for reliable engine operation.....Restrictions on the pressure side of the system will have minimal effect on engine reliability, however, any substantial restriction in the suction side can cause aeration & cavitation......This will spell sure disaster for a race engine at high rpm & can only be avoided by increasing oil delivery to the pump'. [ Italics in original.