This study investigates the potential factors which may cause cylinder bore distortion in V6 aluminum engine block with cast-in gray iron liners. In this research, the microstructure, mechanical properties and residual stress of 319 type aluminum alloy engine blocks were analyzed from top to bottom along the interbore regions in the TSR, T7 heat treated and service (dyno) tested conditions. The results suggest that the cooling rate increased significantly along the cylinder in the vicinity of the chill plate at the bottom of the engine block. This caused a significant refinement in the microstructure which increased the hardness and tensile strength at the bottom of the cylinder relative to the top. The increased strength at the bottom of the cylinder prevented the rapid relief of residual stress at elevated temperature, which suggests that the bottom of the cylinder is less susceptible to cylinder distortion.