There is a Thread on Grumpy's site I started just on Racing Oils Gunny.
Just for super abusive Racing Use.
Stuff like Nitrous Power adders & Turbocharging .
Did alot of research including Vintgage GM Service manuals I have.
GM Specified 20w oil back in the day for abusive race use.
And real Hot summertime high speed driving.
10w30 was for cool weather use.
1970 Pontiac Specified straight 30w or 10w40.
20w50 flows easier than straight 30w.
Viscosity index is lower 20w.
I have used 20w50 Vavoline VR1 in the T/A in the past with no issues. It liked it.
Buzzed 7-8 K rpms like nothing.
Not online , no one ever copied the info from Vintage GM Musclecar service manuals.
In section 1 under Lubrication Guidelines.
I will add more to my thread on Grumps soon.
Royal Purple 20w50 is best their is. Super High Phosphorus & Zinc Content.
Expensive. 6 quarts is $104 Summit Race.
Getting 6 more quarts soon.
Trans Am will hold 11 quarts oil total. Building for Super Battle.
Take down guys like Koolaid.
Let the Fuckers Whine & Cry.