A dual exhaust system does not necessarily increase fuel economy. The main purpose of a dual exhaust system is to improve engine performance by allowing spent gases to exit the engine more quickly. This can lead to a small increase in power and torque, but it won’t have a significant impact on fuel economy. In fact, if your car wasn’t designed for a dual exhaust system, installing one could actually decrease fuel economy. That’s because the extra weight of the second exhaust pipe and muffler can reduce the car’s efficiency. If you’re looking to boost your vehicle’s mpg, there are other modifications you can make that will be more effective than adding a second exhaust pipe.