Straight flow mufflers have no backpressure so you gain at least one mile per gallon, which equates to 1000 gallons saved for every 100,000 miles driven. This is the best, most economic-performance addition you could add to your truck. Since the flow is not restricted, the muffler gathers no soot or condensation, lasting the life of the truck. These mufflers are made to go up the side of the cab or the rear of the bunk. It is a vertical muffler and does not fit W-900-L Kenworth or Internationals