Fiesta ST Boost Control

Getting To Know How The Fiesta ST Controls Boost

Applicable Vehicle:

  • Ford Fiesta ST
    • 2014-2018

Ford's Fiesta ST has an updated style of wastegate control that is designed to regulate wastegate based on throttle inlet pressure (TIP), Compressor outlet pressure (COP), and various measures of boost error.  Our strategy doesn't necessarily change the form of control from load to pressure, we simply relieve some of the limiters that would prevent using a consistent boost pressure out of the way.  
We've found in the past that the perception of consistent power delivery was via a boost reading.  People want to see 20psi, 25psi, etc... regardless of how the performance was.  We're trying to lessen the weight this perception with education but it's a long process.  For now, we still utilize some of the limiters to ensure unsafe conditions cannot be achieved while maintaining fairly consistent boost levels.
There is no real target per-say, you will set a limit using the TIP Ceiling and dial in the wastegate to stay under that maximum at a level you determine.  If atmospheric conditions change enough to where you would overboost, the ceiling will act as your safety and close the throttle to maintain maximum pressure.  In the future you'll be able to fine tune this ceiling with a 3D based table, much like we've implemented in the Focus ST.
Boost levels are determined by the desired load.  Desired load is created by determining desired airflow.  Desired airflow is created by determining desired torque.  Desired torque is created by the throttle requested torque tables along with combining all necessary accessory torque levels and multipliers.
With your turbo example, you would define a desired torque curve through your requested torque tables along with defining proper load translations in the Torque to Load tables.  From there you would create an appropriate wastegate table to achieve those values under all conditions.

Related Links

-Ford Tuning Guide

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