Hydraulic roller oil?

B3RE said

It depends on the lifters. Some tight tolerance lifters don't use viscosity ratings for oil recommendations, but instead use a centistoke value. Try to find an oil with a centistoke of less than 100, and it should work for most lifters on the market.

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^^^^^^^THIS^^^^^^^^^

Some of the newer lifters are designed to use a thin oil.

I know in my testing, before these new lifters were being made with tighter tolerances, more power and RPM came from using a 50 grade oil. Anything less and power started dropping.

With the newer lifters you don't need that grade of oil.

I still hate hydraulic lifters.