I run 5-30 and like it! It is the weight that the engine builder recommended. Plenty of
oil pressure (30 to 35 hot plus 10 psi every 1000 rpm). It was in the car when my wife tore open the
oil pan and quickly drained the motor, while it was running of course. When I was changing the pan I inspected the bearings and cut open the filter. Bearings looked like new and no debris in the filter, pan (or what was left of it), nor pump.
DV was running the stuff when testing DVII on a skid pad. No one seemed to notice, until the motor started making noise near the end of the day, that the
oil pressure was 0 while doing the skip pad testing! Damage was minimal even though the oiling system allowed all the oil to fill up the outside valve cover and the pump was sucking nothing but air. He feels as though the damage would have been much more substantial had he not been using Mobil 1. He has a post on it some where here but that is how I recall it.
I am going to have to go with Bob on this one, run the lightest oil that give you the pressure that you need and of course, ask your engine builder.
All the synthetics are good products, but again, do not run strickly racing oil unless you care to change it weekly. Run multi-vis. No harm in it. I have a 5 -30 and when cold the oil pressure is something like 70 or 80 psi at fast idle!
Those by-pass filter systems look great! I will have to give them some more thought. Now I just use K&N and change it a couple of times a year, oil complete change once a year.
Many of us should, but probably don't, have a thermostat in the oiler cooler lines. It is on my list of things to look into!
Rick