Originally Posted by Dragoneye
I found this on the L92 (the 6.2 L Casull was talking about) engine info page, which is said to be the base for the LS3
The Vortec 6.2L brings GM Powertrain’s industry first cam-in-block variable valve timing (VVT), or cam phasing, to the small block V8. VVT eliminates the compromise inherent in conventional fixed valve timing and allows a previously unattainable mix of low-rpm torque, even torque delivery over a broad range of engines speeds, and free-breathing high-rev horsepower.
The cam-phasing system in the Vortec 6.2L is similar in concept to that introduced in GM’s 3.9L and 3.5L V6 car engines for 2006. The 6.2L’s dual-equal cam phaser adjusts camshaft timing at the same rate for both intake and exhaust valves. A vane-type phaser is installed on the cam sprocket to turn the camshaft relative to the sprocket, thereby adjusting the timing of valve operation.
The vain phaser is actuated by hydraulic pressure from engine oil, and managed by a solenoid that controls oil pressure on the phaser. The phaser uses a wheel or rotor with four vanes (like a propeller) to turn the camshaft relative to the cam sprocket, which turns at a fixed rate via chain from the crankshaft. The solenoid directs oil to pressure points on either side of the four phaser vanes; the vanes, and camshaft, turn in the direction of the oil flow. The more pressure, the more the phaser and camshaft turn. The Vortec 6.2L’s new E38 engine control module (below) directs the phaser to advance or retard cam timing, depending on driving demands. The dual-equal phaser can turn the camshaft over a range of 31 degrees relative to the cam sprocket (or 17 degrees advance, 45 degrees retard relative to the crank).
The benefits are considerable. 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 can advance 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 compromise 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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