Bel-Ray Thumper Racing Works Synthetic Ester 4T Engine Oil is a 4-stroke synthetic racing engine oil developed for full competition use and designed to withstand extreme racing conditions. Fully synthetic ester based base oils withstand the highest temperatures and stresses and provide the ultimate performance for 4-stroke engines. Meets API SN and JASO MA2 requirements. Suitable for air-cooled / liquid-cooled 4-stroke engines and wet clutches.