An exhaust system assembly including a catalyst housing, a catalyst core, and a swirler tube positioned inside the catalyst housing. The swirler tube has a plurality of openings that permit radial exhaust flow into an inner volume of the swirler tube from the catalyst housing. One end of the swirler tube has blades that extend inward and include oblique surfaces arranged at oblique angles relative to a centerline axis of the swirler tube. These blades induce a vortex in the exhaust gases exiting the first swirler tube end. The swirler tube is arranged inside the catalyst housing such that a sequential flow path is created where the exhaust gases flowing through the catalyst housing must first pass through the openings in the swirler tube and then by the blades at the first swirler tube end.