These special lifters (again, the one here is from a truck engine) deactivate on command and are found on cylinders 1, 4, 6, and 7 of the L99 and any other AFM-equipped LS-series engine. When commanded by the LOMA, they mechanically switch so that while the roller continues to follow the cam lobe profile, no motion is transmitted to the pushrod. --->
Interestingly, the use of AFM probably accounts for at least part of the L99's slightly reduced projected power output compared to the LS3, as the system (at least in its current form) creates issues from a valvetrain design perspective. "With AFM, there are design considerations you have to put into the lifters, the camshaft, the other components. You don't want to get into problems with valves deactivating at the wrong time or losing control of the valvetrain," says Rydzewski. "So there are things we do on such an engine for the sake of controlling the AFM." As a result, the L99's fuel cutoff is not as high-around 6200 rpm, versus 6600 for the LS3-and the camshaft specs out with a bit less lift (and reduced overlap) versus the bumpstick in its 6.2L brother.
This brings us to the L99's other feature that sets it apart from the LS3: Variable Valve Timing (or more appropriately, "dual-equal cam phasing"-intake and exhaust valve timing cannot be altered independently). Though it's been in use for a few years on Gen IV truck engines, the L99 represents the first appearance of VVT in a car application. Consider this: if you've ever "degreed" a cam in a small-block-LS or otherwise-you know that in general, advancing cam timing improves output at low rpm, while retarding cam timing improves high rpm performance. The VVT system is able to continuously vary how the cam is phased in relation to the crankshaft while the engine is running, acting within a fraction of a second. The system therefore allows a best-of-both-worlds approach to output by eliminating the compromise between low-end torque and top-end horsepower inherent in fixed cam timing. This is true regardless of whether you're talking about part- or full-throttle operation. There are other benefits to VVT as well: for example, it allows a smoother idle (via fully advanced valve timing events), and in addition to its own role in increasing fuel economy, it also allows the AFM system to function over a broader operating range.
The front-mounted vane-type camshaft phaser is the heart of the L99's VVT system. Operating off of a varying oil pressure signal, it turns the camshaft relative to the cam sprocket, thereby changing the cam's phase relative to the crankshaft. A so-called actuator solenoid valve is used in lieu of a cam bolt, and it gets its instructions from a corresponding computer-controlled unit mounted in the L99's special front engine cover. Oil-pressurized inside the hollow front portion of the cam thanks to a feed hole in the second journal from the front-acts upon the phaser's vanes. The more oil pressure the actuator solenoid valve permits the vanes to experience, the more the cam is turned. While this setup is from a truck engine, the system found on the L99 will be similar. --->
Finally, compared to the LS3, the L99's compression ratio is slightly lower (around 10.4:1), basically dictated by the design of the top of the piston: while the LS3 features flat-tops, the L99's pistons have a recess in the vicinity of the exhaust valve to accommodate valve movement sans contact. This might seem a bit odd considering the L99 cam's lower lift, but it just goes to show you how drastically the VVT system can alter cam phasing. It will be interesting indeed to see how well these technologies perform on the road with the L99-and how the Camaro will fare with its even more technologically advanced base engine, the LLT.