In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders[1] and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern overhead valve and overhead camshaft engines, the cylinder head is a more complicated block often containing inlet and exhaust passages, coolant passages, valves, camshafts, spark plugs and fuel injectors. Most straight engines have a single-cylinder head shared by all of the cylinders and most V engines have two cylinder heads (one per bank of cylinders).