Composite core for the casting of engine head decks

A method for the high pressure die casting of an engine block assembly having at least one cast in place cylinder bore in the engine block and a closed head deck surface, and the resultant engine block are disclosed. This closed deck high pressure die cast engine block assembly will preferably have at least two cast in place cylinder bores in the engine block formed by using a composite core of salt core material supported by at least one cylinder bore to be cast in place. The cylinder bores have a lower outer surface preferably defining at least one surface area that interfaces with the engine block during casting such that the at least one cylinder is cast in place in the engine block. An engine block water jacket—as defined by the salt core portion of the composite core—will preferably provide an open passage between each cylinder bore such that water may flow around and entire outer circumference of the upper outer surface of the cylinder bores. This provides better and more uniform cylinder wall cooling, reducing thermal hot spotting and bore wall distortion.