Breathing Right Helps Chevrolets Get More From Less

Variable Valve Timing improves drivability and fuel economy while reducing emissions

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May 06, 2011, 01:02 ET

PONTIAC, Mich., May 6, 2011 /PRNewswire/ -- Athletes understand that proper breathing is critical to maintaining peak performance under all conditions and so do Chevrolet powertrain engineers. Getting air in and exhaust gases out of the combustion chamber under all speeds and driving conditions is essential to outstanding drivability and fuel efficiency with low emissions.

"Whether powered by four, six or eight cylinders, virtually every current Chevrolet car and truck from the compact Aveo and Cruze to the full-size Suburban SUV features variable valve timing (VVT) on its engine to optimize its breathing," said Sam Winegarden, General Motors executive director of Global Engine Engineering.

The camshafts are driven by chains from the crankshaft to keep the valve opening in sync with the motion of the pistons in the cylinders.

Through continuous adjustments of the camshaft phasing, engineers can achieve smoother idle control without sacrificing the ability to breathe at higher engine speeds. This ability contributes to the 3.6-liter V6 in the Chevrolet Camaro generating 312 horsepower while getting an EPA-estimated 30 mpg on the highway.

Chevrolet's VVT system uses a hydraulic mechanism to twist the camshaft relative to the crankshaft position so that the valves can be opened and closed earlier or later. On dual overhead cam engines such as the Ecotec inline-four and the 3.0 and 3.6-liter V6, the intake and exhaust cams can be adjusted independently, allowing the valve overlap – the time that intake and exhaust valves are both open – to be varied as well.

The 60 degrees of camshaft adjustment available on the turbocharged 1.4-liter Ecotec that powers the Cruze enabled engineers to eliminate the conventional exhaust gas recirculation system to simplify the overall engine packaging – the way the engine fits in the car – and still reduce emissions.

"Bookending the Chevy lineup, the VVT-equipped Cruze Eco achieves an EPA estimated 42-mpg highway while the full-size Silverado XFE pickup is estimated at 22 mpg highway, both of which are best-in-class figures for their respective segments" said Winegarden. "In fact, the 2011 Cruze Eco is the most fuel efficient gasoline-fueled vehicle in America."

Founded in Detroit in 1911, Chevrolet celebrates its centennial as a global automotive brand with annual sales of about 4.25 million vehicles in more than 120 countries. Chevrolet provides consumers with fuel-efficient, safe and reliable vehicles that deliver high quality, expressive design, spirited performance and value. The Chevrolet portfolio includes iconic performance cars such as Corvette and Camaro; dependable, long-lasting pickups and SUVs such as Silverado and Suburban; and award-winning passenger cars and crossovers such as Spark, Cruze, Malibu, Equinox and Traverse. Chevrolet also offers "gas-friendly to gas-free" solutions including Cruze Eco and Volt. Cruze Eco offers 42 mpg highway while Volt offers 35 miles of electric, gasoline-free driving and an additional 344 miles of extended range. Most new Chevrolet models offer OnStar safety, security and convenience technologies including OnStar Hands-Free Calling, Automatic Crash Response and Stolen Vehicle Slowdown. More information regarding Chevrolet models can be found at www.chevrolet.com

SOURCE General Motors