I posted a long time ago here that the only time I run a 50 grade oil with hydraulic lifters. Which means you have to open the bearing clearances up just to run that goo. But that's what the lifters wanted. Dyno testing hydraulic rollers on the dyno with a 5w30 oil and we were just fighting the pig. So I threw in some junk 20w50 we had there and the RPM came back, the valve train was much more quiet and power was up across the RPM range.
That was almost 20 years ago. That's also when I stopped using hydraulic roller lifters. I can run a solid roller on a HRT lobe and it works much better. Don't need goo for oil. Don't have to run Godzilla wide clearances.
All the cool people now tell me the "new and improved" hydraulic lifters now have "precisely machined internals" that allow precise oil control and let's you use a 30 or even 20 grade oil with them.
I'll never know because if I have to build an engine with any kind of hydraulic lifter I won't do it.
