Our Ballade Sports Exhaust Manifold features 5 step piping size with each step helping in anti-reversion, and also backing up of exhaust flow. Weighing at 12lbs less than stock (OEM is 25lbs), the primary runners are 1.75 inch, to 1.875 inch, to 2.00 inch, to 2.25 inch, to 2.5 inch merge collector. Stepping the header pipe size helps direct flow and increase scavenging, thus allowing for a faster exit. The S2000 firing order is cyl 1-3-4-2, therefore our runner design is sequential, creating a venturi effect. This application fits standard factory catalytic converter location. Wheel horsepower gains are approximately 10whp mid-range dependent on application setup.