Active valve lift system

The I-Active Valve Lift System (AVLS) (i stands for intelligence) is a valvetrain technology implemented by Subaru in the 2.5L naturally aspirated engines to improve emissions, efficiency and performance. Note that AVLS is different from AVCS used on other Subaru engines. AVLS improves performance or efficiency by changing which camshaft is operating which of the two intake valves. The camshafts on all AVLS Subaru engines have specially designed lobes for intake valves. They feature two different cam profiles: a low/mid lift profile or a high lift profile. The two intake valves in each cylinder are operated by a rocker arm with its own cam lobe. The cam utilized is selected by the Engine Command Unit (ECU). To select different valve lift modes, oil pressure generated by the engine moves a pin which locks the two lobes together. At low engine speeds the low/mid lift camshafts increases the speed of air rushing into the engine thereby increasing torque and efficiency. At higher engine speeds the high lift camshafts reduce resistance to incoming air by getting the two intake valves wide open. This reduces resistance to intake air and improves power. It should be noted that AVLS only operates one of the intake valves in each cylindar as the other is always open to promote swirl. It is not clear at what RPM or engine load the two camshafts operate as it has not been disclosed by Subaru. But independent testing by Subaru owners indicate that the engines operate mostly in high lift profile mode. Low lift profile operation is limited to very low loads and or below a maximum engine speeds of 2500rpm.

External links

• Subaru Drive Magazine articles: i-AVLS