Injection Window Modification
When using direct injection it is common for the injection window to support post-ignition injection. This can be used in specific operating conditions such as cat heating where raw fuel is injected into the cylinder at the end of the power stroke. In stock configuration the N54 supports injecting from 540° to -180° of ignition angle (in red below). For this reason our fuel injection window is offset by 180° (in green below). So an injection angle of 0° is actually -180°. This is fine for direct injection but presents problems when the engine is converted to port injection.
Leaving this 180° offset while using port injection presents a problem as 720° to 0° of injection would result in part of the fuel mass being used for one combustion event and the rest for the next combustion event due to the intake valve closing. For this reason we offset the fuel injection window (in green below) by -180° from the ignition angle (in red below). This adjustment means that 0° of fuel injection window represents when the intake valve has closed and fuel can no longer make it into the combustion chamber for that combustion cycle.
When NXM Port Injection is enabled we automatically apply this offset to the Start of Injection tables. So 720° in the Start of Injection table results in injection starting at 720° of engine position relative to the fuel injection window (in green above). This is much more intuitive for users and tuners.