I would stay with at least 25% total oil, and 28 to 29% preferred. I ran an ABC Fox on 22% half and half castor synth., for a while, and the wrist pin bosses wore out pretty quick. This was one of the earliest ones, so don't know if they have been improved or not. Not much bearing surface for the wristpin in the aluminum piston. They sure do run nice on profiles with that setup though.