Any motorcycle style 4 stroke synthetic or semi-synthetic should be okay as long as it says it was design for such application with wet clutch compatibility. Some companies like Amsoil and Motul speciallize in these. I've run the motul techno-synthetic and would swear by it in my Raptor. Smells sweet, works even better, running an abused to hell '01 Tranny and I can't blow it up with that oil in it, put that in since the very first oil change. I have some Amsoil I'm going to try too, but I think I'm going to stick with the Motul if it doesn't seem significantly better. They specifically design their synthetic oils and blends to work with wet clutchs in ATV's and motorcycles. I should know what happens when you use the bad automotive kind that ain't so friendly to wet clutches, I burnt out a set in my 200ES Big Red trike and my '94 T-Wolf, but can't burn out my '01 Rappy clutch for the life of me with the right oil!