Spectro's Heavy Duty Golden semi-synthetic motor oil represents a significant improvement in High Performance motor oils. Conventional all-mineral oil formulations offering high film strength provide only minimum cleanliness, since heavy carbon petroleum-base stocks are used to achieve extra protection. With Heavy Duty Golden semi-synthetic, the need for these heavy mineral oils is eliminated through the use of a complex synthetic that exceeds even the heaviest petroleum oils in film strength, providing a level of protection previously unattainable. The semi-synthetic petroleum blend is a 20W50 formulation specifically for the large air-cooled Harley-Davidson engines. Enhanced additive technology yields improved wear, rust and oxidation resistance, and ensuring longer engine life. Heavy Duty Golden semi-synthetic is rated to the highest possible API service classification SG, and is strongly recommended for all Big Bore, Stroker and High Performance Harley-Davidson engines including gas or alcohol burning Drag-Race motors. This very same oil is used by Scott "The Z-Man" Zampach winning the Harley-Davidson championship in both the AMA U.S. Twins and AMA C.C.S. Twin Sport races without any engine failure.