The Mercedes S 350 CDI 235hp (W221 - 2005 - 2013) produces 235bhp and 540Nm in standard form. Our Stage 1 ECU tuning file raises output to 290bhp and 620Nm, a gain of 55bhp and 80Nm, with no hardware modifications required. The file is delivered through the ByteFLASH portal and is ready to write to the vehicle.