A monolithic aluminum block using a newly developed Al-20%Si alloy was made by a vacuum die-casting process. The bore surface design was a sleeveless type with uniformly dispersed primary-Si crystals around 20μm. The die-casting technology consists of a highly airtight die with two series of evacuation systems. The vacuum level in the die cavity was determined to be as low as 5kPa. The gas content of the block was found to be as low as 5cc/100g Al, which has enabled T6 heat treatment. The die cavity temperature was carefully controlled to generate a fine dispersion of primary-Si crystals. The engine testing has proved that the bore wall temperature is 30 K lower than that of the aluminum block enclosing a press-fitted cast iron liner. The superior cooling performance has decreased the oil consumption value to one half that of the aluminum block enclosing a cast iron liner. The simulation has revealed that the Si exposure provides EHL contact in an exposure height ranging from 0.15 to 0.3 μm. The wear on the bore surface occurs in the process comprising the initial wear of the exposed Si crystals to 0.15 μm and a subsequent steady state where the exposure height becomes constant.