Multi-valve

In automotive engineering, an engine is referred to as multi-valve (or multivalve) when each cylinder has more than two valves.

All tappet-valve, four-stroke internal combustion engines have at least two valves per cylinder â€" one for intake of air and fuel, and another for exhaust of combustion products. Adding more valves improves the flow of intake and exhaust gases, potentially improving combustion efficiency, power, and performance. Simply using two larger valves does not work because of the circular shape of the combustion chamber and the need for valves to be round, which gives a lot of unused space; four (or more) smaller valves can replace the largest single valves which could be fitted into the space and have a greater effective area.

Most multivalve engines use an overhead camshaft to actuate the valves, and many use double overhead camshafts (DOHC). However this is not always the case: Chevrolet recently introduced a 3-valve version of its Generation IV V8 which uses pushrods to actuate forked rockers, and Cummins makes a 4-valve pushrod straight-6 Diesel, the Cummins 600.