4 - inch constant - diameter DPF - back. Improves flow up to 50 Percent and cuts backpressure up to 40 Percent, allowing the engine to produce more horsepower. Includes Huge Polished Chrome or Cerakote Black Patented SideKick tip. Reducing backpressure allows the engine to expel spent gasses with less effort. Less pumping loss means more horsepower, lower EGTs, and improved fuel economy. The Monster Exhaust system cools while flowing up to 50 better than stock Cooling without killing flow is a major challenge. But the Monster Exhaust wins on both counts thanks to its mandrel - bent constant - diameter tubing and huge Ob - Round patented SideKick tip. The tip is the key. Its unique shape mixes hot exhaust gas with cool ambient air. And, it keeps your trailer safe by directing exhaust gasses to the side. US Patent 5,581,111 S1