An exhaust gas treatment device includes an inlet housing having an inlet opening for receipt of an exhaust flow from an engine aligned along a first axis. A main housing includes a cylindrical body portion defining a treatment zone and an exhaust outlet aligned along a second axis extending parallel to the first axis. The inlet housing is in fluid communication with and fixed to an outer surface of the main housing. The inlet housing includes a contoured wall including an end portion positioned opposite the inlet opening, an aperture extending through the wall transverse to the first axis, divergent side wall portions on opposite sides of the inlet opening, and a necked portion having a reduced cross-section positioned downstream of the inlet opening and upstream of the aperture. A component is coupled to the main housing for treating exhaust flowing through the treatment zone.