Every major manufacturer now has at least one four valve per cylinder engine in production, and a few brands—such as Honda and Toyota—have applied this technology to nearly all the car engines they sell in the U.S.
That begs the question: Is there anything more, something beyond the four-valve combustion chamber? Audi provided a definitive answer by displaying a 2.2-liter five-cylinder engine at last fall’s Frankfurt auto show with no fewer than 25 valves.
One aim with any multivalve design is to position the spark plug as close as possible to the center of the chamber for optimum combustion. (This is impractical in a two-valve design.) The second benefit comes from the simple fact that additional intake and exhaust valves provide a superior flow path—what engineers call higher volumetric efficiency. Engineers also…
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MotorTrend (Digital) - 1 Issue, January 1991