I have a sbc little M with a pair of 62s journal bearing turbos. It is a street car so see heat soak and idling in traffic. I have morel hydraulic roller lifters .903 diameter and the instructions state no restrictors and no oil thicker then 10W30. Main and rod clearances were accurately measured(not plastigauge) at .0025mains .0025 rods. I have an HV55 pump. When idling in traffic the oil pressure drops to 15-20 PSI. Nothing shows in the filter when I have a look but 15-20 seems a little low to me. The question is what oil is the most stable in regards to viscosity when it gets hot (doesn't get thin).