Even with a fairly low pressure relief spring, the cold oil pressure will spike up above 60 PSI on most engines. After a few minutes of warmup, if it's still over 50 at cruise RPM a lower-pressure relief spring is a good idea. Hot idle oil pressure can be anywhere from 15-30 PSI, sometimes lower. On engines with an idiot light instead of a gauge, the light turns on below 7 PSI. I've seen race engines actually twist the tang off the pump drive shaft if the pressure is regulated at too high a number. It's also rough on the distributor drive gear and the camshaft gear.
Jerry
