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How Does a Combustion Engine's Valvetrain Work?
Take a look at what really happens as the valves usher fuel and air into the engine and let the exhaust out.
This installment of Toyota's Engines 101 series takes a closer look at one of the most critical parts of an engine: its valvetrain. The video establishes what parts comprise a valvetrain, looks at variable valve timing technology, and considers the effect of alternatives to the Otto cycle valve timing scheme, such as the Atkinson cycle.
This cutaway image reveals the secrets of Toyota's 2ZR engine. TOYOTA
About the Author
Dan’s coverage of the auto industry over three decades has taken him to the racetracks, automotive engineering centers, vehicle simulators, wind tunnels, and crash-test labs of the world.
A member of the North American Car, Truck, and Utility of the Year jury, Dan also contributes car reviews to Popular Science magazine, serves on the International Engine of the Year jury, and has judged the collegiate Formula SAE competition.
Dan is a winner of the International Motor Press Association's Ken Purdy Award for automotive writing, as well as the National Motorsports Press Association's award for magazine writing and the Washington Automotive Press Association's Golden Quill award.
Dan, testing the 2025 Aston Martin Vanquish. ANDY MORGAN/ASTON MARTIN
He has held a Sports Car Club of America racing license since 1991, is an SCCA National race winner, two-time SCCA Runoffs competitor in Formula F, and an Old Dominion Region Driver of the Year award winner. Co-drove a Ford Focus 1.0-liter EcoBoost to 16 Federation Internationale de l’Automobile-accredited world speed records over distances from just under 1km to over 4,104km at the CERAM test circuit in Mortefontaine, France.
He was also a longtime contributor to the Society of Automotive Engineers' Automotive Engineering International magazine.
He specializes in analyzing technical developments, particularly in the areas of motorsports, efficiency, and safety.
He has been published in The New York Times, NBC News, Motor Trend, Popular Mechanics, The Washington Post, Hagerty, AutoTrader.com, Maxim, RaceCar Engineering, AutoWeek, Virginia Living, and others.
Dan has authored books on the Honda S2000 and Dodge Viper sports cars and contributed automotive content to the consumer finance book, Fight For Your Money.
He is a member and past president of the Washington Automotive Press Association and is a member of the Society of Automotive Engineers.
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