Multi-valve
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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 — 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.
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.
History
The first multivalve engine was built by Peugeot in 1912 for Grand Prix racing. The technology was also attempted by Bugatti, Bentley, and Stutz, but it was not until the 1970s that this technology became widespread. The first example of the era was by Jensen in the 1972 Jensen Healey roadster, which used a Lotus developed version of a GM design which resulted in a 1973 cc (2.0 L) DOHC engine that delivered 140 hp. Other early implementors included Cosworth (on the 1975 Chevrolet Vega's 2300 engine), Lotus Cars (on the 1976 Esprit — which used a 160 hp version of the same engine first seen in the Jensen Healey), and BMW (on the 1979 M1's M88 engine). Triumph also introduced a single overhead cam 16-valve head on the Slant-4 in their Dolomite Sprint.Ferrari soon introduced their own multivalve design with the Quattrovalve 308. From there, Honda and Toyota brought the technology to the mainstream in the 1980s.
Modern multivalve engines
Today, multivalve engines are used by nearly all manufacturers. They are common among the Japanese and European makers. The US manufacturers have lagged, though improvements to their pushrod designs have caused some to question the benefits of multivalve engines.General Motors began using 4-valve DOHC heads with their Quad-4 and Northstar engines in the 1990s. The company worked with Lotus, a subsidiary at the time, to adapt two pushrod engines for 4-valve DOHC cylinder heads: The LT5 V8 from the Corvette ZR-1 and the 3.4 L LQ1 V6. Pushrod engines are still the norm at GM, however.
Ford's DOHC success came with their (multivalve-optional) Modular V8, SHO V6, and Mazda-developed B-family of I4 engines. Their Duratec family now consists entirely of multivalve engines, and is used across the product line.
DaimlerChrysler's Mercedes-Benz used 3-valve SOHC engines for many years, but recently switched to 4-valve designs. Their American counterpart, Chrysler, has developed a number of successful multivalve OHC I4 and V6 engines, but relies on pushrod V8s.
VAG companies like Volkswagen and Audi now use 5-valve engines in many of their vehicles after acquiring the technology from Bugatti who developed it for their EB110 supercar. EDIT: Toyota also use 5-valve heads in their 4A-GE power plants. Sk 'silver top' 4.gen 160ps(hp) and 'black top' 5.gen 165ps(hp). Built from ~1991 to 1999. In dyno tests they are claimed to not give more than 150hp or so. Ferrari has 5-valve tech as well.
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