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how motorcycles work.com knowledge is power. 5-valve head. Exhaust valves spark plug intake valves note the different angle piston connecting rod outer valves inner valve angle In order to be actuated by the same camshaft (although, obviously different lobes) the inner valve must be tilted at a slightly different angle than the outer two valves. camshaft 3 intake cam lobes valve spring buckets note how the inner valve is at a slightly different angle than the outer two. View from top spark plug hole diameter of cylinder base 3 intake valves blended into 1 port. intake air/fuel. If 2 intake valves provide better airflow and cylinder filling, why not try 3 intake valves? YAMAHA did just that with their GENESIS motor series. For many years the 5-valve (20-valve, 4-cylinder) was used. Among the variations were a 750cc engine and a 1000cc engine used in the renowned Yamaha R1. Certain technical challenges are encountered with 5-valve heads. Cycle World did a write-up on this in 2007 when Yamaha went to a 4-valve head on their revised R1. Intake valve size and layout obviously affect cylinder filling, turbulence, swirl, and combustion flame propagation. Engines can be designed for good flow and cylinder filling at low rpm and make useful torque at such speeds, but may struggle to fill the cylinder effectively at higher speeds. Or valve shape and protrusion into the combustion (continued)