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In an internal combustion engine, the cylinder head (often informally abbreviated to just head) sits above the cylinders on top of the cylinder block. It consists of a platform containing the poppet valves, spark plugs and usually part of the combustion chamber. In a flathead engine, the mechanical parts of the valve train are all contained within the block, and the head is essentially a flat plate of metal bolted to the top of the cylinder bank with a head gasket in between; this simplicity leads to ease of manufacture and repair, and accounts for the flathead engine’s early success in production automobiles and continued success in small engines, such as lawnmowers. This design, however, requires the incoming air to flow through a convoluted path, which limits the ability of the engine to perform at higher revolutions per minute (rpm), leading to the adoption of the overhead valve (OHV) head design, and the subsequent overhead camshaft (OHC) design.