I will add to dogdays acurate lecture that he is correct on all of his points, you can trim the spring so it wll have 65 lbs of pressure at 6500 RPM with hot oil and it will have 80 lbs when cold at or close to 1500 RPM and above I have seen a 10 HP gain at 5900 RPM with 30WT oil at 170 F oil temps by reducing the oil pump spring free length(cut a coil and half off of it ) which reduced the oil pressure at 5900 RPM to 65 lbs at 170 F oil temps, same motor, 20 minutes apart on each pull with no other changes When using 5W20 WT oil on later dyno tests I saw no differences in HP with the oil temps at 110 F versus 190 F at 80 lbs pressure With 30 WT there was 10 HP difference between 130 F and 170 F at 80 lbs pressure, hence the later tests to reduce oil pump drag by reducing the bypass pressure, free HP