A system and method are disclosed for improving the performance of an aftertreatment system by elevating its temperature above an activation temperature. According to at least one aspect of the present disclosure, the method includes injecting a quantity of a fuel into certain fueled cylinders of a plurality of combustion cylinders of an internal combustion engine, the plurality of combustion cylinders further including non-fueled cylinders. Exhaust from the fueled cylinders is directed through the aftertreatment system while uncombusted gas from the non-fueled cylinders is directed away from the aftertreatment system. In certain embodiments, the uncombusted gas may be directed into an intake manifold in fluid communication with the plurality of combustion cylinders through an orifice. The system includes an engine having exhaust valves to control flow of the exhaust and uncombusted gas and a controller configured to perform the operations of the method.