There will be many opinions... I swear by Brad Penn Grade 1 20w50 for race engines partial synthetic "The Green Oil". Others will say Royal Purple... I think for racing you'll want the protection of a synthetic blend or straight synthetic but the stuff ain't as cheap as straight mineral petroleum (which isn't very cheap anymore either).

You'll lose some power with the heavier oil but it protects components better than like a 10w30

In my previous motor I had good luck with Castrol GTX...

Two cents from my experience and those of other customers of my engine guy that use the stuff...

-Chris