A system and method for treating exhaust gasses from an engine is described. In one example, the exhaust gasses are routed from the engine to atmosphere through a helical exhaust passage. The helical exhaust passage includes a plurality of spatially separated exhaust passages that separates the exhaust flow into separated smaller flows, wherein the smaller flows are re-introduced into a common passage and re-combined to form a single exhaust flow, and wherein the plurality of spatially separated exhaust passages induces a helical flow pattern within the re-combined exhaust flow.