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Oh, and the rule of thumb for required oil pressure is 10 psi per 1000 rpm. So for a worn motor with 30 psi oil pressure at 50 mph the maximum rpm you want to operate at is 3000 so a car like that should be fine on secondary roads but will blow up on the highway.
Just to clarify this "rule of thumb." This number (10psi/1000rpm) is OK for a nominal 3.000in main bearing diameter. For a Packard V-8 with 2.500in mains, the number would be ~8.3psi/1000rpm (2.5/3.0). For example, a Pontiac 421/428/455 with 3.250in main bearings, the value is ~11psi (3.250/3.000). The early small block Chebbies had a 2.300in main journal and could get by with 7.6psi/1000rpm.
The reason for this is that the oil pressure has to overcome the centripetal force of the oil in the internal passage from the bearing surface to the centerline of the crankshaft before any oil can reach the rod bearings.
Packard service manual lists the "Normal oil pressure" as 45-50psi at 2800 rpm. Obviously, this is more than enough pressure to overcome the main bearing centripetal back pressure.
The above is probably more than you wanted to know, but I thought I would lay it out here anyway.
Craig
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