Kevin, I don't want to send you in an unjustified direction, but it would not hurt to measure the "crankcase", or internal pressure of the engine at 3000-4000 RPM. This is NOT related to
Oil pressure. Engines generate a certain amount of pressure from naturally imperfect cylinder sealing, and crank rotation. That's why engines require venting. I use a vacuum/pressure gauge placed on the
oil filler tube. There is usually a cone-shaped rubber adapter that accompanies your compression gauge that provides a good seal. Hold the gauge tightly on the tube, while someone throttles the engine. The big block experts can suggest a maximum allowable pressure, but I would say the pressure will be zero if your venting system is adequate. Remember that flow is no greater than the smallest orifice within your vent system. You can have 3/4" tubing, but restricted flow due to the internal diameter of the fittings. Again, experienced big block guy's may be rolling their eyes over this reply, because there is a common problem associated with 427's that I am not aware of. Many of the big block engines I see have braided or rubber lines from each ventilated valve cover cap routed to a small capture tank mounted on the firewall to insure there is no internal pressure. Don't get whacked out over this suggested cause for your
oil leak! Just check to see that your present venting method isn't causing excessive crankcase pressure. These forum threads have to be carefully vetted! Everybody has THE answer!y