Since I started racing mine I ve been using Valvolene ATV 10w40 . I change it after every race and its been working great . No slippage, coming out clean . I have a sponsorship offer from Amsoil but it would still cost me $8 a quart . Ill stick with Valvolene . 17 races x $8.00 x 3 = a ton of $$$$$$$ . My stuff cost $4 a quart