>>20724637The material you described would be a poor choice for a gasket, both the block and cylinder head are going to expand when the engine gets hot and contract again when it cools. Heat-resistant materials wouldn’t expand as much as the aluminum of the engine block and head and potentially cause loss of compression and/or gasket failure over many heating/cooling cycles.
The second reason is the two matting surfaces of the assembly are never going to be 100% even, there will always be regularizes in the two areas, a gasket made of a more pliable material helps fill the micro-gaps between the two surfaces.
