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In automotive engineering, an engine is referred to as multi-valve (or multivalve) when it has more than two valves.
All internal combustion engines have at least two valves - one for intake of air and fuel, and another for exhaust of combustion products. Adding more valves increases the flow of intake and exhaust, potentially improving combustion efficiency, power, and performance.
Most multivalve engines use an overhead camshaft to actuate the valves, and many use dual overhead cams. 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.
History
The first multivalve engine was built by Peugeot in 1912 for Grand Prix racing. The technology was also attempted by Bugatti and Bentley, but it was not until Honda built the SOHC 4-valve Honda S600 that a multivalve engine was available to the general public. However, at 606cc and producing only 57bhp at an extremely peaky 8500rpm, the engine was much more popular in Japan than it was in the west.
Many more manufacturers adopted the technology with dual overhead cams in the 1970s. The first was Jensen in the 1972 Jensen Healey roadster. This used a Lotus developed version of a GM design which resulted in a 1973cc (2.0 liter) DOHC engine that delivered 140bhp. Others, including Cosworth (on the 1975 Chevrolet Vega's 2300 engine), Lotus Cars (on the 1976 Esprit - which used a 160bhp 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 followed Lotus and GM in to the multivalve designs with their Quattrovalve 308. From there, Honda and Toyota rapidly spread the technology to their mainstream models 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 American 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 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 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 Chrysler operation 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.
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