An aftertreatment module for use with an engine is disclosed. The aftertreatment module may include a housing having an inlet configured to direct exhaust in a first flow direction into the aftertreatment module, and an outlet configured to direct exhaust in the first flow direction out of the aftertreatment module. The aftertreatment module may also include a catalyst bank separating the inlet from the outlet. The catalyst bank may have a face disposed at an oblique angle with respect to the first flow direction. The oblique angle may create an inlet passage extending from the inlet to the catalyst bank and having a decreasing cross-sectional area, and an outlet passage extending from the catalyst bank to the outlet and having an increasing cross-sectional area.