Heavy-duty fleets in need of a muffler that can do it all - reduce back-pressure, improve driver comfort, increase fuel efficiency and resist corrosion - can have it all with the Walker Mega-Flow™ muffler. Manufactured and marketed by Tenneco Inc., the Walker Mega-Flow muffler addresses key fleet needs by reducing exhaust system back-pressure and improving fuel efficiency versus OE exhaust systems without impacting acoustic performance.