The 50 Series HD Heavy Duty Muffler is appropriately named, a tough customer just like the trucks it was designed for. With 4.00-inch internal components and large case size, these mufflers help to significantly increase mileage, torque, and horsepower while greatly improving towing power acceleration. The 50 Series Heavy Duty is great for all gas and diesel applications, and late-model trucks used in the most extreme working conditions.