The BMW Z4 3.5i - N55 - Twinscroll - 306hp (E85 - 2003 - 2008) produces 306bhp and 400Nm in standard form. Our Stage 1 ECU tuning file raises output to 350bhp and 520Nm, a gain of 44bhp and 120Nm, with no hardware modifications required. The file is delivered through the ByteFLASH portal and is ready to write to the vehicle.