Well, to be honest, I am not sure... My engine builder just broke in my new 404 with Joe Gibbs break-in oil last week, and just switched out the light break-in valve springs for the racing springs today.
He is switching me to Joe Gibbs racing oil but I am not sure which grade yet...? I will find out tomorrow when I pick the new bullet up after final run-in.
I had been running Mobil 1 synthetic for years, but he wants JG in this new Dart engine...
Jim