Cylinder Head Assembly: Description and Operation
CYLINDER HEADDESCRIPTION
Single overhead camshaft aluminum alloy cylinder heads have two intake and one exhaust valve per cylinder.
OPERATION
The cylinder heads, having three valves per cylinder minimizes exhaust port surface area, keeping more heat in the exhaust stream to provide fast catalytic converter heating for low emissions and to reduce cooling load. A three-valve configuration also simplifies the engine by allowing use of one cam per bank rather than two and provides room in the combustion chamber for two spark plugs that provide more complete combustion. Valves are set at an included angle of 35.5°, forming a shallow combustion chamber. A central passage in each head that connects with each cylinder delivers either assist air or recirculated exhaust if needed to reduce exhaust emissions. The camshafts turn directly in the head; no bearing inserts are used. Transverse coolant flow within the head provides optimal cooling of the exhaust valve seats while minimizing heat extraction from the exhaust ports to enhance catalytic converter warm up.