Ejector assemblies and engine systems have a pressure regulator in fluid communication with an ejector. The pressure regulator receives boost pressure and selectively allows the boost pressure to pass through a valve opening therein under selected engine conditions and into the ejector as regulated boost pressure. Both the pressure regulator and the ejector each have a conduit defining a passageway that includes a Venturi gap separating the passageway into a converging section and a first diverging section that both narrow toward the Venturi gap. The pressure regulator has a piston operatively connected to a valve mechanism positioned for movement therewith to control the passage of the boost pressure through the valve opening, and the valve mechanism defines a passage therethrough that includes a gradually narrowing portion that is narrower than the valve opening.