Variable Valve Timing
The Gen IV Vortec 6.0Ls bring GM Powertrain’s industry exclusive cam-in-block variable valve timing (VVT), or cam phasing, to the small block V-8. 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 6.0Ls is similar in concept to that introduced in GM’s 3.9L and 3.5L V6 car engines for 2006.
The Vortec 6.0L’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 both intake and exhaust valve operation. The vane 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 6.0L’s new E38 engine control module (below) directs the phaser to advance or retard cam timing, depending on driving demands. The dual-equal phaser system has the authority to retard the camshaft by up to 52 crankshaft degrees.
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, allowing 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.
Finally, cam-phasing helps maximize the fuel-saving benefits of Active Fuel Management technology (below). The cam phaser can adjust valve-timing for maximum torque when the Vortec 6.0L is operating as a V4, keeping the engine in this fuel-saving mode as long as possible.
The Positive Crankcase Ventilation (PCV) system now incorporates a larger 2.75mm flow orifice and, to aid assembly, has quick-connect fittings for the connections on the engine.
Active Fuel Management
The L76 aluminum-block Gen IV Vortec 6.0Ls feature GM’s Active Fuel Management technology (AFM). AFM temporarily de-actives four of the 6.0L’s cylinders under light load conditions. It increases fuel economy approximately 6 percent under the federal government’s required testing procedure and potentially more in certain real-world driving conditions. Yet truck owners don’t have to compromise on the Vortec 6.0Ls outstanding peak horsepower to go farther on a tank of gas.
Active Fuel Management stems from a simple premise: most truck owners have more power than they need much of the time. Many choose powerful V-8 engines to be prepared for the occasional heavy load, but during routine commuting that powerful engine operates at a fraction of its capability. Volumetric efficiency is impaired, and that means less than optimal fuel mileage. AFM offers a common-sense solution. It saves fuel by using only half of the Vortec 6.0L’s cylinders during some driving conditions, and seamlessly reactivates the other cylinders when a driver demands full power for acceleration or load hauling.
Managed by the new E38 engine control module (ECM), AFM automatically shuts down every second cylinder, according to firing order, during light-load operation. In engineering terms, this allows the working cylinders to achieve better thermal, volumetric and mechanical efficiency and lowering cyclical combustion variation from cylinder to cylinder. As a result, AFM delivers better fuel economy and lower operating costs. Perhaps the most sensible thing about AFM is that it harnesses the engine’s existing capabilities, starting with the potential designed into the E38 ECM. The only mechanical components required are special valve lifters for cylinders that are deactivated, and their control system. Active Fuel Management relies on three primary components: De-ac (for deactivation) or collapsible valve lifters, a Lifter Oil Manifold Assembly (LOMA), and the ECM.
One of the most sophisticated engine controllers, the E38 ECM (below) measures load conditions based on inputs from vehicle sensors and interprets that information to manage more than 100 engine operations, from fuel injection to spark control to electronic throttle control. AFM adds an algorithm to the engine control software to manage cylinder deactivation and reactivation. When loads are light, the E38 automatically closes both intake and exhaust valves for half of the cylinders and cuts fuel delivery to those four. The valves re-open to activate all cylinders when the driver demands brisk acceleration or full torque to move a load. The engine’s electronic throttle control (ETC) is used to balance torque following cylinder deactivation or reactivation. The transition takes less than 20 milliseconds, and is virtually indiscernible to most drivers.
Valve lifters are operated by the engine’s camshaft, and lift a pushrod that operates the valves in the cylinder head. In the Gen IV Vortec 6.0L, the De-ac lifters are installed in cylinders 1, 4, 6 and 7, while the remaining cylinders use conventional lifters. The hydraulically operated De-ac lifters have a spring-loaded locking pin actuated by oil pressure. For deactivation, hydraulic pressure dislodges the locking pin, collapsing the top portion of the lifter into the bottom and removing the ability to lift the pushrod. The bottom of each De-Ac lifter rides up and down on the cam lobe but the top does not move the push rod. The valves do not operate and combustion in that cylinder stops. During reactivation, the oil pressure is removed, and the lifter locks at full length. The pushrods, and therefore the valves, operate normally.
The final AFM component is the LOMA. This cast-aluminum assembly is installed in the Vortec 6.0’s V, or valley, in place of a conventional engine block cover. The LOMA holds four solenoids, control wiring and cast-in oil passages. The solenoids are managed by the ECM, and each one controls oil flow to a De-Ac Lifter, activating and de-activating the valves at one cylinder as required for Active Fuel Management.
The Gen IV Vortec 6.0L’s fuel injectors are identical for all cylinders; those feeding the de-activated cylinders are simply shut down electrically by the ECM during de-activation. When the cylinders are deactivated, the engine effectively operates as a V4. AFM operation is load based, as measured by the ECM using dozens of inputs, overlain with the driver’s demand for power as measured by throttle application. AFM’s response time is measured in milliseconds. Operation is always transparent to the driver. The engine returns to V-8 mode the instant the controller determines that acceleration or load requires additional power.
The benefits are substantial. Active Fuel Management does not effect exhaust emissions, and it reduces overall emissions to the extent that less fuel is used. Further, the savings reflected in EPA numbers may not account for AFM’s full impact. Owners who primarily travel long distances at steady speeds will see further fuel-economy improvements.