A variable compression ratio internal combustion engine and method of operating the same is provided. The engine comprises an engine block defining at least one cylinder; a head connected with the engine block; a piston slidable in each cylinder; a combustion chamber defined by the head, the piston, and the cylinder; an air intake valve movable to open and close the air intake port; an air supply system including two turbochargers in series fluidly connected to the air intake port; a fuel supply system operable to inject fuel into the combustion chamber; an air intake valve assembly comprising a camshaft configured to open the intake valve; and a hydraulically actuated variable intake valve closing mechanism configured to hold the intake valve open.