I have in the past use Kendall GT1, originally 15-40, most lately 10-40. However most recently due to the reformulating and reduction of the
Zinc and Phosphorus I have added some EOS from GM. Next time I'll be using Brad Penn or Joe Gibbs
oil. I began using Kendall while racing high winding 4cylinder engines years ago. It was chosen becazuse they had an excellent anti foaming package. That may have changed.