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how motorcycles work.com knowledge is power. 4-valve head. Blended exhaust port. Exhaust valves spark plug intake valves blended intake port piston. View from top. exhaust valves spark plug hole intake valves. Blended intake and exhaust ports smoothly shape the flow path of two valves into one port, to be connected to fuel injection throttle bodies (intake ports) or exhaust manifold headers (exhaust ports). For performance-oriented engines, 4-valves per cylinder is by far the most common configuration, specifically for high rpm engines designed for high-revving horsepower. 4-valves allow for increased valve area, thus increased flow, thus increased cylinder filling. Also, within the compact space of cylinder head, 4 valves fit nicely around a centrally-oriented spark plug. 2 smaller valves can be lighter and accelerated with less force than a single, larger valve. Thus, cam lobe ramps can be made steeper and greater lift can be utilized, because decreased valve mass helps prevent valve float and allows the valve to be reciprocated up and down faster, allowing for higher rpm and thus more power strokes per unit time. lift cam lobe ramp valve lifter (bucket) camchain sprocket bearing caps valve lifters (buckets) camshaft bearings cylinder head Exploded view of single cylinder head with 4-valves.