Abstract: This invention relates to a method and structure of preventing cylinder head warpage and over-heating of internal combustion engines by utilizing a cylinder head modification assembly. The cylinder head modification assembly includes (1) a main expansion transfer plate assembly; and (2) an exhaust port expansion transfer assembly, each of which are adapted to be mounted on a cylinder head structure to provide strengthening and expansion transfer characteristics. The main expansion transfer plate assembly is of an elongated rectangular shape having various portions of different heights in order to achieve the required strength and heat transfer properties. The exhaust port expansion transfer assembly includes a main support body having an integral anchor section and is adapted to be mounted and secured between adjacent exhaust ports of the cylinder head structure.