Joe Lapine at Danbury Competition Engines built the 428 for my ERA and recommended Valvoline 10W40 when he built it.
I was recently speaking to him about another subject and he changed his recommendation to Honda GL4 motorcycle
oil. Says it's the real stuff.
Changed over to the Honda
oil on the last change but don't have any miles on it yet to give a pro or con. I'll see as I go along but Joe seems to have all of his stuff in one bag and has been building engines for a long time so I'm reasonable confident.
Put over 40K on the Valvoline with the
oil and filter changed every 3000 miles and haven't encountered any failures or problems.
DonC