GM's blurb on the VVT in their newer pushrod V6 engines, which can hardly be called small and which were introduced when the G6 came out. 3.5,3.6,and 3.9 liter engines.
"For all the advanced systems in the 3.5L V6, perhaps the most significant?certainly the one that has garnered the most attention?is variable valve timing (VVT). GM?s new generation V6s were the first cam-in-block engines with VVT?an accomplishment engineers considered extremely difficult, if not impossible, just a few years ago. The 3.5L?s dual-equal VVT uses a hydraulically operated vane-type cam phaser that turns the camshaft relative to its drive sprocket.
The advantages of cam-in-block VVT are pronounced. The cam phaser changes valve timing on the fly, maximizing engine performance for given demands and conditions. At idle, for example, the cam is at the full advanced position. That allows exceptionally smooth idling. Under other operating demands, the phaser adjusts to deliver optimal valve timing for performance, drivability and fuel economy. At high rpm it might retard timing to maximize airflow through the engine and increase horsepower. At low rpm it advances timing to increase torque. Under a light load (say, casual everyday driving), it can retard timing at all engine speeds to improve fuel economy. Without cam phasing, a cam design must be biased toward one strength or another?high-end horsepower or low-end torque, for example?or profiled at some median level that maximizes neither.
Variable valve timing allows linear delivery of torque, with near-peak levels over a broad rpm range, and high specific output (horsepower per liter of displacement) without sacrificing overall engine response, or drivability. It also provides another effective tool for controlling exhaust emissions. Because it manages valve overlap at optimum levels, it eliminates the need for an Exhaust Gas Recirculation (EGR) system. "
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