The Synthetic oils burn cleaner -- Less smoke --- I will not buy any oil that is Refined from Penn. Crudes,,, It is loaded with Parafin. I bought a used Car that the valve Covers when pulled you could not even see the tops of the rocker arms for the Valves. the drain holes were stoped up and leaking into the cylinders making lots of smoke. The Previous owner was proud he had only used Quaker State