|Looking for the most aggressive sound in the Flowmaster muffler line? Then take a look at these 40 series Flowmaster mufflers. Designed for use on street and strip vehicles, they take the sound waves produced in the exhaust, and cancel them against angled baffles built into the muffler case. This improves both horsepower and fuel economy. Best of all, these Flowmaster mufflers allow you to hear that cool Flowmaster tone inside of the vehicle, as well as outside of it. So, if you want more power and less noise, then you've gotta get these Flowmaster mufflers.