I know all oils are NOT the same. All of the off the shelf oils don't have any anti friction modifiers anymore because of the EPA. My machinist prefers I use Brad Penn for flat tappet engines and Schaeffers oil in my roller motors.
I run Brad Penn green oil in my GP because I don't have a catalytic converter so the ZDDP can't ruin it.
The fact is royal purple is garbage oil I've seen more scored bearings and spun bearings when people use it. When it gets hot it turns to tar. Its not much of a problem in our cars cause the motors aren't working as hard as my pull truck or race engine. If you ever lugged the motor for a period of time it would cause problems. Its just overrated synthetic with some purple dye in it and the dye is what causes problems I think.
If you don't believe there is any difference in oils buy some good oil and some off the shelf oil put some on your fingers and rub them together. You will feel the difference in film thickness.
