Ignition MBT Reference
Overview
Selects the ignition table that represents MBT (Minimum Spark Advance for Best Torque).
MBT is defined as the ignition timing that produces the maximum engine torque for a given engine speed and load operating point. Additional ignition advance beyond MBT will typically provide little or no increase in torque, while ignition timing retarded from MBT will result in a reduction in engine torque output.
ℹ️ Why is MBT Required?
The ECU Engine Torque Model requires a reference for the ignition timing that produces maximum engine torque at each engine speed and load operating point. The selected MBT reference table provides this reference and defines the maximum available engine torque for the Engine Torque Model.
By comparing the active ignition timing against the MBT reference table, the ECU can determine when the engine is operating below its maximum torque potential due to ignition retard and apply the appropriate correction to the calculated engine torque.
The ECU continuously calculates the difference between the active ignition timing and the configured MBT reference table:
Where:
- 0° Offset = Engine operating at MBT torque.
- Negative Offset = Ignition timing is retarded relative to MBT, resulting in a reduction in the ECU calculated engine torque.
- Positive Offset = Ignition timing is advanced beyond MBT and will typically result in little or no increase in engine torque.
Options
| Value | Mode |
|---|---|
| 0 | Off |
| 1 | Table 1 |
| 2 | Table 2 |
Off
Disables MBT referencing. The Engine Torque Model assumes no torque reduction due to ignition retard.
Table 1
Uses Ignition Table 1 as the MBT reference table.
Table 2
Uses Ignition Table 2 as the MBT reference table.
ℹ️ Recap
When the MBT Offset becomes negative, the active ignition timing is retarded relative to the MBT reference timing. As a result, the ECU determines that the engine is operating below its maximum torque potential and applies a corresponding reduction to the calculated engine torque used by the Engine Torque Model.
The MBT reference table should represent the ignition timing required to achieve maximum engine torque.
If dual ignition tables are used for different fuel types, such as Petrol and E85, the ignition table representing the highest achievable engine torque should generally be selected as the MBT reference table.
Since E85 typically requires greater ignition advance to achieve MBT than an equivalent Petrol calibration, the E85 ignition table will often be the preferred MBT reference.