Spent some time trying to find out what is in XP3. Closest explanation is "proprietary". That doesn't say much. Not knocking it but that "word" is way over used.Just as an example, Castrol does not own oil refineries, oil wells, etc. and does nothing more than blend numerous products from numerous vendors to make numerous blends of oils.Unless you are trying to extract every bit of HP from your combo, 20W50 is the best weight for racing. It is very forgiving, filling voids better than 0W10. Other than high end 500 + miles road race cars, 20W50 keeps all those motors alive in conditions that a drag motor will never see.