A filter cartridge assembly comprising: a filter cartridge cage defining a filter chamber; a pleated filter assembly secured in the filter chamber having alternating folds including an inner set of folds and an outer set of folds and constructed from a filter material having a defined thickness, wherein the pleated filter assembly has a top end and a bottom end, wherein the distance between the two ends defines the axial length of the pleated filter assembly, wherein the filter assembly has a longitudinal axis, and wherein each fold defines a substantially linear apex substantially parallel with the longitudinal axis; and, a filter core having a core wall that defines a core outlet, wherein the filter core is secured in the filter chamber surrounded by the pleated filter assembly, wherein the apexes of the inner set of folds register against the core wall, characterized by the core wall defining a plurality of through-bores, wherein the perimeters of the through-bores are formed with regular and irregular geometric cross-sectional shapes including at least one peninsula extending inwardly from the through-bore perimeters toward through-bore center points, the through bores having center points and modified perimeter shapes that differ from round through-bores, but that maintain the same area as the area of a round through-bore having a specified area, wherein extension portions of the core wall that define the plurality of modified perimeter through-bores extend into central areas of the modified perimeter through-bores to reduce the radial distances between the through-bore center points and the extension portions relative to a radius of a round through-bore having the same area as the modified perimeter through-bores. a filter cartridge cage defining a filter chamber; a pleated filter assembly secured in the filter chamber having alternating folds including an inner set of folds and an outer set of folds and constructed from a filter material having a defined thickness, wherein the pleated filter assembly has a top end and a bottom end, wherein the distance between the two ends defines the axial length of the pleated filter assembly, wherein the filter assembly has a longitudinal axis, and wherein each fold defines a substantially linear apex substantially parallel with the longitudinal axis; and, a filter core having a core wall that defines a core outlet, wherein the filter core is secured in the filter chamber surrounded by the pleated filter assembly, wherein the apexes of the inner set of folds register against the core wall, characterized by the core wall defining a plurality of through-bores, wherein the perimeters of the through-bores are formed with regular and irregular geometric cross-sectional shapes including at least one peninsula extending inwardly from the through-bore perimeters toward through-bore center points, the through bores having center points and modified perimeter shapes that differ from round through-bores, but that maintain the same area as the area of a round through-bore having a specified area, wherein extension portions of the core wall that define the plurality of modified perimeter through-bores extend into central areas of the modified perimeter through-bores to reduce the radial distances between the through-bore center points and the extension portions relative to a radius of a round through-bore having the same area as the modified perimeter through-bores.