The 2006-09 factory returnless fuel system incorporates an in-tank fuel pressure regulator.
The ScienceofSpeed In-Tank Fuel Pressure Regulator is a factory original Denso fuel pressure regulator with increased relief spring pressure that increases fuel rail pressure by approximately 2-4 PSI to increase fuel flow 3-5%.
2006-09 supercharged and turbocharged S2000s with the original returnless fuel system can experience marginal fuel system performance when boost pressure nears 10 PSI. This inexpensive drop-in replacement for the factory fuel pressure regulator gives a small bump in fuel delivery (3-5%) which is enough to improve fuel system performance to a safe margin.
For applications over 12 PSI / 425 BHP, we recommend converting to return fuel system.