Bel-Ray Thumper Racing Synthetic Ester Blend 4T Engine Oil Bel-Ray Thumper Racing Synthetic Ester Blend 4T Engine Oil is a 4-stroke motorcycle racing oil that combines the finest quality synthetic esters and highly-refined mineral base oils specifically engineered for todays 4-stroke single cylinder, multi-valve racing engines. Provides maximum anti-wear protection for valve-trains, rings, cylinders and pistons. Delivers maximum horsepower while providing consistent clutch performance. Meets API SM and JASO MA2 requirements. Suitable for air-cooled/liquid-cooled 4-stroke engines and wet clutches.