Bore-up series adds 1mm in diameter to the inner cavity of the cylinder for a larger volume of air that can support a longer barrel (and greater power). High precision laser-cut cylinder and taper cylinder head means that these components are engineered to 4/1000 tolerance for utmost smoothness and power. If you want to assemble an VSR10 with the maximum possible power potential, then this cylinder set is right for you. Note that the tolerance level and precision of these parts far surpasses most parts on the market (for comparison, Laylax cylinders have a tolerance level of only 1/100, a tenth of the tolerance of PDI's laser cut parts) so is the choice for professional and serious tuners in Japan. Note that moving to a bore-up configuration requires you to upgrade to a larger bore-up receiver, which accomodates this larger cylinder.