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There are two injection events per cycle; the first one is right after the exhaust valve closes to pre-cool the inlet charge in combustion chamber and cylinder. This helps improve volumetric efficiency and results in a cooler chamber that is less likely to suffer from detonation even with the LT1's high compression ratio. This first pulse also forms a cylinder filled with a lean fuel-air mixture.
The second pulse comes late in the intake cycle as the piston is moving towards TDC. This results in a stratified, richer mixture around the spark plug for reliable ignition while achieving a leaner burn. When the engine is starting from cold, fuel is injected later, closer to the time of the exhaust valve opening, so the extra hot exhaust gasses can light off the catalytic converter faster. This is significant because cold start emissions before the cat lights off contribute to more than 90% of the total emissions created by a car during the FTP cycle used for emissions certification.
The AFM system cuts hydraulic pressure to special roller lifters, which causes them to collapse to deactivate the cylinders. A lightweight spring on the lifter acts like a lost motion device to hold everything together when the lifter is deactivated.
In previous versions of AFM used in lower performance variants of the LS, the rpm was limited to the low 6000 rpm range due to the increased mass of the lifter. For the LT1, Chevy engineers worked endlessly to increase the stiffness of the valvetrain while pairing mass, allowing the system to work to the 7000 rpm range.
The most noticeable difference is the cam phaser wheel in the front of the cam so the ECU can sense cam position for the variable cam timing system. Another difference is the triple lobed cam lobe on the back of the cam that drives the high-pressure direct injection fuel pump.
