[WorkinLonghorn]

Originally Posted by 72SB

OP

if your new "GM Crate motor" is a hydraulic flat tappet cam motor (like your original motor was) you need to run an oil with high zinc content or a zinc additive with conventional oil ESPECIALLY if this is a brand-new flat tappet hydraulic cam motor.

If its a newer "full" roller hydraulic cam, then conventional oil is fine and no zinc additive or high zinc oil is needed....although it never hurts. Motor oil stopped containing high levels of zinc when CATS came out, conventional or diesel oil as zinc kills CATS.

regarding your 15-40 diesel oil, the weight is not an issue although weight depends on how main bearing clearances are set up. Stock original motors are typically 10-30 but often performance build motors have a "slightly" wider bearing clearance so 20-50 is spec so there is a bigger oil wedge between crank and bearing for higher than 5500 rpm use.

For flat tappet hydraulic cam or solid lifter motors I use Valvoline VR1 racing oil as it has high zinc content in 10-30. Joe Gibbs oil also

Thanks for this. The engine is just like stock except I believe they lowered the compression from 9-1 to 8 or 8.5-1 (can't remember). So it has the flat tappets with the usual very modest 3.90"/4.10" valve lift. It operates below 2,500 RPM unless I'm really pressing to get up a freeway on-ramp or hauling considerable weight. Maybe I'll get some additive this one time until I change it again. -BA

P.S. Bearings are very tight with Oil pressure ~30 PSI at hot idle.