Originally Posted by www.gmpowertrain.com

The Vortec 3.7L I5 carries over the VVT (variable valve timing) or cam phasing system employed on the 3.5L I-5, which was one of the world’s first truck engines with this technology. The cam phaser changes exhaust cam lobe timing relative to the cam-drive sprocket, which in turn varies exhaust valve timing on the fly, maximizing engine performance for given demands and conditions. At idle, for example, the exhaust cam is at the full advanced position for minimum intake-valve overlap. That allows exceptionally smooth idling. Under other operating conditions, the phaser adjusts to deliver optimal exhaust-valve timing for performance, drivability and fuel economy. The result is 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. Because it manages valve overlap at optimum levels, cam phasing also eliminates the need for an Exhaust Gas Recirculation (EGR) system.

As was the spline-piston phaser, the new vane phaser is actuated by hydraulic pressure from engine oil, and managed by a solenoid that operates to a calibrated duty-cycle. Yet the operating mechanism is different. Instead of a helical spline and piston, the vane phaser uses a wheel with four vanes (like a propeller) to turn the camshaft relative to the cam-sprocket. The solenoid directs oil to pressure points on either side of the four vanes; the vanes, and camshaft, turn in the direction of the oil flow. The more pressure, the more the phaser and camshaft turn. Like the previous phaser, the vane phaser turns the Vortec I5’s camshaft a maximum 24 degrees relative to the sprocket.