Boost Control

Applies To:

  • BE5 EJ206, EJ208
  • BH5 EJ206, EJ208
  • GC8 EJ207
  • GF8 EJ205, EJ207
  • SF5 EJ205

These ECUs use closed-loop boost control to manage turbo output and engine power.

Algorithm

Closed-Loop Control

  • Sample manifold pressure, RPM, Throttle position
  • Calculate desired boost target using RPM, throttle position, ECT, IAT, Atmospheric pressure
  • Compare to measured manifold pressure
  • Make adjustments to wastegate solenoid duty cycle as necessary
  • Repeat every 120 ms (~8.3 times per second)

Improvements

Map Interpolation

Some of the orginal boost control maps did not use interpolation. This causes sudden changes to the Boost Target and Wastegate Duty Cycle which can be problematic when trying to achieve better turbo spool and operating higher boost targets close to the limits of the engine or turbo. The firmware has been modified to add interpolation to the following maps:

Single Turbo ECUs:

  • Boost Target
  • Wastegate Duty Cycle - Base
  • Wastegate Duty Cycle - Maximum
  • Wastegate Duty Cycle - Overboost Step
  • Wastegate Duty Cycle - Underboost Step
  • Wastegate Duty Cycle - Overboost Step (Transition)
  • Wastegate Duty Cycle - Overboost Step (Transition)

Twin Turbo ECUs:

  • Boost Target - Primary
  • Boost Target - Secondary
  • Wastegate Duty Cycle - Primary Max
  • Wastegate Duty Cycle - Secondary Max

Proportional Correction (Single Turbo Only)

The factory wastegate algorithm can be compared to a PID controller with only the integral (I term) enabled. The wastegate output is increased or decreased by a pre-set amount with multiple updates until the boost target is reached. In practice this results in slow turbo response when the initial wastegate duty value is far from what is necessary to reach the boost target. The step amount can be increased but is also prone to causing boost target overshoot or boost oscillation around the target.

We have patched the firmware to add a proportional (P) term to the algorithm. This allows making large changes to the duty cycle instantly resulting in faster turbo spool and quicker corrections to prevent boost spikes.

Boost Control - Proportional Correction Enable
Set to '1' to enable proportional boost control.

Overboost/Underboost Step (Transition)
When proportional boost control is enabled, these maps are used to lookup the proportional error term of the calculation. The Error index values are still shared with the other Overboost/Underboost Step maps so any changes to the index will affect the other maps too.

Boost Control - Wastegate Duty Integral Limit
When proportional boost control is enabled, this limits the positive and negative magnitude of the integral term of the calculation. For example, a value of 10% will limit the wastegate duty integral term to between -10% and +10%.

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