The camshafts on an AVLS-equipped engine have specially designed lobes for intake valves. They feature two different cam profiles:
- A low/mid-lift profile
- A high-lift profile
Which cam profile is utilized is regulated by the Engine Control Module (ECM) computer. The AVLS-equipped Subaru engines use oil pressure generated by the engine to activate the different valve lift settings:
- At low engine speeds, the low/mid-lift profile increases the speed of the air rushing into the combustion chambers from the intake ports. The net result is an increase in torque, which gives you more pulling power.
- At high engine speeds, the cam lift is switched to the high-lift profile to reduce resistance to air coming into the engine. At high speeds, this allows the engine to breathe deeply and generate strong horsepower for ease of passing at highway speeds.
AVLS-equipped Subaru engines have two intake valves per cylinder. But AVLS only controls one of them. The other always operates in the high-lift mode. This results in an imbalance in pressure as air enters the cylinder, which creates a swirling pattern. The turbulence provides a better distribution of the air-fuel mixture at low engine rpm, which translates into more even combustion. The ECM automatically selects the different cam lift profile settings based on engine load, driving requirements, and atmospheric conditions.
For the 2007 model year, the i-Active Valve Lift System is standard on all 2.5-liter naturally aspirated Subaru engines. In essence, AVLS provides two engines under your hood – one tuned for optimum fuel economy and one tuned for performance – and both deliver very low levels of emissions.