A system for improving the fuel economy of a vehicle includes an engine configured to produce an initial exhaust gas, a first exhaust pipe connected to the engine, a start catalyst connected to the first exhaust pipe and a second exhaust pipe connected to the start catalyst. The system also includes a bypass exhaust pipe connected to the first exhaust pipe and the second exhaust pipe and a valve positioned at one end of the bypass exhaust pipe and configured to move between a closed position and an open position for directing the initial exhaust gas to the start catalyst and/or the bypass exhaust pipe. The system includes an electronic control unit that is used to control the first valve to be in the closed position or the open position based on an estimated temperature of the start catalyst.