An exhaust system includes a first aftertreatment substrate configured to receive exhaust gases from an engine and a second aftertreatment substrate downstream of the first aftertreatment substrate, wherein the first aftertreatment substrate is smaller than the second aftertreatment substrate. A bypass valve is configured to direct exhaust gas through the first aftertreatment substrate prior to entering the second aftertreatment substrate when an exhaust gas temperature is below a predetermined temperature and is configured to allow exhaust gas to bypass the first aftertreatment substrate and enter the second aftertreatment substrate when the exhaust gas temperature is above the predetermined temperature.