I mentioned in another thread, I am sure KC will recognize it, but what he said about base stocks appears to be the only difference between Synpower and Napa Syn. Looking at the pds for both, you would notice that the cold pumping viscosity for synpower is a little better than napa, a little thinner at very cold temps. Ashland does claim to use 5-10% group IV oil in Synpower as part of the basestock. They do not claim this for NAPA. That would explain the difference in cold pumping. Otherwise, the TBN, antiwear additives etc are close enough to be identical to each other. So in my opinion, in short, Synpower is Group III and IV mixture, and NAPA is all group III, there is your price difference.
Side note: I have used both, and really liked both but I really loved the NAPA sales. Used them in a frontier, direct injection 4.0, a little hard on oil and both of the oils held up really well out to 5k miles, I wouldn't use any oil past that in that vehicle because of timing chain issues that can occur. Anyways, use either oil with confidence, look on our UOA section you will see very many good UOA reports with napa.
