"All engine oils are made up of a base oil & an additive package. Conventional engine oils use a base oil that is derived through a conventional refining process. These oils fall into 3 different groups based on their purity level and their viscosity index. The group I oils contain the highest level of impurities and the lowest viscosity index. Group II base oils have lower levels of impurities but the same range of viscosity index values. Group III oils have a low impurity level but they also have a better viscosity index. Due to the fact that some high quality group III oils (a.k.a. hydro-cracked) can have most of the characteristics of group IV oils,the National Advertising Department of the Better Business Bureau has allowed oils manufactured from group III base stocks to be SOLD as synthetic. However,many companies in the performance lube industry still disagree with this ruling."(Dsport magazine march issue #39 )
Group IV & V base oils are not solvent-refined base oils. Instead,these oils are polymerized base oils or TRUE synthetics.
I have made a list of "TRUE"synthetics. If your favorite oil is not on the list I'm sure it's a good oil,just don't kid yourself. It may not be as good as you may have been lead to believe. And I doubt you will ever find them on the shelf at Wall-Mart.
Also check out this link.
Motul 300VPower Racing
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