Description 16V 4age – TRD head gasket Genuine Tokyo Technocraft product that has a thickness of 0.8mm and features a heavy duty 4-layer metal construction.   Compression ratio change Due to being of a thinner construction this part raises the static compression ratio by approximately 0.5:1 when used in place of the original Toyota head gasket.   Bore size compatibility These gaskets have a bore opening diameter of 82.6mm, this would suggest that they are compatible with up to a 1mm (82mm) piston size.   Engine compatibility CAN NOT be used on a 20V 4AGE due to the different cooling system configuration.