I've ran 4 different oils this year, on alky injection with a primer plus
15/40 shell stuff looked good going in .. didnt look so hot coming out
20/50 & 10/30 vr1 -- little to no difference other then 5 hundreths on the track
and whats in there now is 5w/40 syn castrol, a buddy of mine did some r&d on this stuff, and oil temp is very good under hard use. So far so good.