Engine cylinder block cast with component zones having different material properties

A cylinder block for an internal combustion engine, comprising a unitary iron casting having a number of component zones, with each of said zones having a selected surface to volume ratio and a selected section thickness sufficient to cause in-mold cooling during the casting process at controllable, but varying, rates sufficient to result in different percentages of nodular and compacted graphite iron in at least two of the zones of the cylinder block, with at least one of said zones comprising a box beam main bearing bulkhead having a hollow core of variable volume, so as to permit adjustment of the surface to volume ratio of the bulkhead without altering the outer dimensions of the bulkhead.