In a thread from a few months ago I questioned whether the testing for NOACK has changed with SP/GF6. Valvoline's 5w20 went from having among the lowest NOACK values for a 20 weight oil currently available with their SN PLUS versions and now all of a sudden they are
I presume to think that there is more to this story that simply has not been revealed for public consumption. I surmise that testing has changed and the definitive results are just not available as of yet, however, the approved oils likely passed some preliminary screening to make sure that they passed the industry benchmark for NOACK being 15%.
My understanding some were given Provisional SP GF-6A because of a backlog of testing. Of course if they fail when actually tested it will be rescinded.
Also the standards for the Fuel.Conserving part of the equation I thought had increased (Some conflictng info for GF-6A on this). If so the easiest way to do it would be lower viscosity base oils and more VII. This would result in an oil that technically passed the viscosity requirements yet had increased temporary shear resulting in less.power loss.
Of course my understanding may be flawed.