The Mercedes S 350 CDI BlueTec 258hp (W221 - 2005 - 2013) produces 258bhp and 620Nm in standard form. Our Stage 1 ECU tuning file raises output to 300bhp and 700Nm, a gain of 42bhp and 80Nm, with no hardware modifications required. The file is delivered through the ByteFLASH portal and is ready to write to the vehicle.