Here's Pennzoil 's product data sheet for their Synchromax. It says it's made from paraffinic base stocks. So not synthetic, but with high lubricity. Compared to Valvoline, the cold viscosity is a little thinner and the hot viscosity is a little thicker. That's explained by the viscosity index number, which is quite a bit higher than Valvoline's. I must have been wrong in assuming there is some synthetic base oil in the Valvoline based on viscosity index. Simply put, the higher the viscosity index, the less a lube will thin when heated. I'd use the Pennzoil in any street application.
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