Question: what is the difference between bmw z4 3.0i and 3.0si?
Answer: The 3.0Si, which was the uplevel performance model (but below the wicked Z4 M's 330bhp) used the same motor, but with a variable-length intake manifold, and a more aggressive ECU tune. Output in the 3.0Si is 255bhp and 220lb-ft of torque, compared to the 3.0i's 215bhp and 185lb-ft.