Bel-Ray Thumper Racing Works Synthetic Ester 4T Engine Oil Bel-Ray Thumper Racing Works Synthetic Ester 4T Engine Oil is a 4-stroke synthetic motorcycle racing oil that has been developed for full works competition use and is designed to withstand extreme racing conditions. Full synthetic ester base oils withstand the highest temperatures and stresses and provide the ultimate performance for 4-stroke motorcycles. Features: Synthetic ester formula for the ultimate thumper experience that withstands extreme racing conditions For air-cooled/liquid-cooled 4T engines with wet clutches API SN, certified Jaso MA2