“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 engine’s camshafts are driven by chains from the crankshaft to keep the valve opening in sync with the motion of the pistons in the cylinders. By always adjusting their phasing, engines can run smother, even at idle, without sacrificing performance at higher speeds.
Thanks to the technology, the V6-powered Chevrolet Camaro can put out 312 horsepower while delivering an EPA-estimated 30 mpg on the highway.
Meanwhile, the 60 degrees of camshaft adjustment available on the turbocharged 1.4-liter Ecotec that powers the Cruze allowed engineers to do away with the exhaust gas recirculation system, simplifying the construction process, while also reducing emissions.
In the case of 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.
“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.”
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