redgreen: IMO additives for oils are nothing more than snake oil. some folks swear by them but modern lubricants are so good now i personally don't see a need for additives. regarding car oils in H-D products and Buells, i've known alot of guys who have run car oils such as castrol gtx in their v-twin motors for years with no problems whatsoever. the primary/trans on a buell is a different story requiring a different lubricant with an entirely different additive package. primary/trans oils such as motul, bel-ray, amsoil, silkolene have a totally different additive package such as modifiers for sheer resistance, friction modifiers to add longevity to the clutch pack, things of that nature. our buell motors run pretty damn hot especially in the summer so alot of guys on here use full synthetic 20-50 in the motors including myself.