Originally Posted by colyneedsv8
I'm 99% sure there are NOT special lobes for AFM.
Nope, its true...those 4 cyl cam lobes are slightly different. I will try to find article that mentions it (Hot Rod?) as GM doesn't care cause you would only replace with another stocker.Some light reading right from GM on one engine:
2007 Vortec 5.3L V8 (LMG)
The next-generation Vortec 5.3L V8 is standard in the all-new Avalanche SUT and Suburban and Yukon XL full-size sport-utility vehicles. It is optional in the Tahoe and Yukon full-size sport-utility vehicles and the New Silverado and Sierra pickups . In all applications, the Vortec 5.3L is installed with GM Powertrain’s Hydra-Matic 4L60 four-speed automatic transmission.
The Vortec 5.3L has been the most popular Vortec V8 and it offers technology for every truck buyer’s needs: Powertrain’s industry leading Active Fuel Management technology, cast-iron engine block, and E85 flex-fuel capability are features on the (LMG). These engines are the fourth-generation descendents of one of the most important and successful engines in automotive history—the original Chevrolet small-block, which debuted in 1955. The Gen IV Vortecs feature technology the creators of the first small block could not have imagined, yet they share one fundamental trait with the original: a market-leading balance of performance, sophistication, economy and durability.
The first Gen IV Vortec V8 (LH6) was introduced for model year 2005 in GM’s mid-size sport-utility vehicles.
SAE Certified Power rating
SAE certification is a voluntary power and torque certification procedure developed by the SAE Engine Test Code committee and approved March 31, 2005 . This procedure (J2723) ensures fair, accurate ratings for horsepower and torque by allowing manufacturers to certify their engines through third-party witness testing to the SAE J1349 standard. Refer to the horsepower / torque plots in this section.
Gen IV Cylinder Block
The Gen IV cylinder block shares two key design elements with GM’s original small block V8: a 90-degree cylinder angle with 4.4 inch bore centers. Beyond that, the latest small block applies design, casting and machining technologies that were unfathomable in the 1950s.
The Gen IV block debuted in 2005 as the foundation for the 400-hp LS2 V8 in the Chevrolet Corvette, Cadillac CTS-v and Pontiac GTO. The new Vortec truck block applies all the improvements in the LS2, tailored for the demands of truck application.
It was developed with the latest math-based tools and data acquired in GM’s racing programs, and it an exceptionally light, rigid foundation for an impressively smooth engine. Its deep-skirt design helps maximize strength and minimize vibration. The bulkheads accommodate six-bolt, cross-threaded main-bearing caps that limit crank flex and stiffen the engine’s structure. A structural oil pan further stiffens the powertrain.
The new-generation small block is cast with oil ports in its V, or valley, to accommodate advanced technologies in the Vortec 5.3L, including Active Fuel Management (AFM) cylinder deactivation. The Lifter Oil Manifold Assembly (LOMA), a key component of AFM, installs in the valley in place of a conventional engine block cover. As a result, knock sensors located in the valley on the Gen III V8 have been moved to the outside of the engine block, while the cam sensor has been moved from the rear of the block to the front cover.
The Vortec 5.3L is offered with either a conventional cast-iron block (LMG), or an aluminum engine block (LC9), giving customers a choice and allowing technology appropriate to the application. The lighter aluminum block allows vehicle engineers more latitude in tailoring weight distribution, and can mean a slight improvement in fuel economy. The Gen IV aluminum block is cast from A356-T6 alloy, with pressed-in iron cylinder liners. It weighs roughly 100 lbs. less than a comparable cast-iron engine block.
Active Fuel Management
All Gen IV Vortec 5.3L V8s feature GM’s industry leading Active Fuel Management technology (AFM). AFM temporarily de-actives four of the 5.3L’s cylinders under light load conditions. It increases fuel economy 7 percent under the federal government’s required testing procedure and potentially more in certain real-world driving conditions. Yet truck owners don’t sacrifice superior V8 power and performance 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 V8 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 5.3L’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 by reducing heat loss, combustion loss and friction, 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. The incremental cost for the customer is nominal per engine. 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 extant, the E38 ECM (below) measures load conditions based on inputs from vehicle sensors and interprets that information to mange 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 can’t be detected by the driver.
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 5.3L, 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 contact with 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 5.3’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 5.3L’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 varies with oil temperature, but in all cases is measured in milliseconds. Operation is always transparent to the driver. The engine returns to V8 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 will reduce overall emissions significantly 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 substantially greater fuel-economy improvements. GM expects 2 million vehicles with Active Fuel Management on the road by 2008.
The exhaust system for the Gen IV Vortec 5.3L required careful tuning to maintain optimal noise and vibration control. In four-cylinder operation, the engine creates second-order exhausts pulses; in eight-cylinder operation, in creates fourth-order exhaust pulses. The system requires special pipe tuning to account for both.