Each intake valve is operated via rocker arm by its own camshaft lobe – one lobe with a high profile and the other with a lower profile. The resultant staggered valve openings increase the speed of the air entering the combustion chamber, which increases torque.


The rocker arms of each cylinder’s two intake valves are locked together, and the high-profile camshaft lobe operates them both. The two wide valve openings reduce resistance to intake air, helping to improve horsepower. 

AVLS is one of the keys to the power and efficiency found in today’s 2.5-liter naturally aspirated Subaru BOXER engines.


Contemporary Subaru engines deliver more performance per liter than their predecessors while operating with dramatically reduced emissions. One key to these advancements is the development of computer-controlled systems. Computers provide new levels of management in a wide range of areas -- from the amount of fuel injected into the combustion chamber to transmission shift functions.


The Role of Camshafts


On all four-stroke engines (which power the great majority of the vehicles on the road today), camshafts open and close intake and exhaust valves by the shape of their cam lobes. In the past, modifying an engine to deliver more horsepower entailed physically disassembling the engine and then installing a new camshaft with different cam lobe profiles. The only trouble was that engines “tuned” for maximum horsepower allowed other attributes to suffer. They tended to have rough idles and/or reduced fuel economy.


Today, thanks to the power of the computer and AVLS, modern Subaru engines deliver the best of all worlds -- performance, economy, and low emissions. (The i in the name i-Active Valve Lift System stands for intelligent -- meaning the system automatically responds to the driving and atmospheric conditions to deliver optimum performance.)


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