Originally Posted by SubieRubyRoo
So, forgive my non-chemist mind here, but looking at page 5 of the Chevron PPT would lead me to believe that any oil with a VI above 170 is using a good portion of mPAO? This would then lead one to reason that mPAO is the main reason we typically see Noack increase WRT VI.
Do oils with regular PAO do better on Noack test than mPAO? Not that I buy into all of it, but that information would be good for the GDI folks who think Noack is the end-all, be-all of oils for their engines.
Oh, no, I doubt any engine oil, other than racing oils, uses mPAO. Even if it does, the amount would have to be very small to still meet the W spec, and you wouldn't see much effect other than a small boost in the viscosity.
You obtain a higher VI by putting more VII. This also requires the base oil to be thinner, which in turn increases the Noack. It's not necessarily bad news for GDI engines, as it's the base-oil quality, not the Noack, that really matters since the intake-valve deposits are caused by the liquid PCV mist, not distilled vapor.