Boost Control Explained

Boost Control Explained

A guide on how to use the Elite Boost Control Function for typical street or mild racing use.

What is a Wastegate?

A wastegate, by it's namesake, is a gate that lets waste gases of the motor bypassing the turbine.  If no wastegate is present, all of the exhaust generated by the motor would enter the turbine.  This would drive the turbine with more energy which in turn would drive the compressor to generate boost pressure.  More boost pressure generates more exhaust pressure, which drives the turbine harder which drives the compressor harder, and around in circles we go until something gives.   The wastegate allows the exhaust pressure to be regulated, so that only an amount of exhaust pressure required for the compressor to generate a certain amount of boost is allowed to reach the turbine.  This regulation is achieved by using a mechanical valve that can open to vent exhaust pressure between the motor and the turbine and instead send it to the exhaust system or open air for some applications. The opposite end of the valve is connected to a diaphragm. To keep the valve closed there is a spring that pre-loads the valve against its seat and altering the spring pressure will change the default boost pressure.

 Typical turbocharger configuration

A hose connection from the compressor housing provides boost pressure to the valve side of the diaphragm.  When the boost pressure exceeds the spring pressure the valve will open and begin venting pressure. This will regulate the turbine pressure and hence the boost pressure.

How does Boost Control work?

To allow boost to be adjusted higher than the spring pressure, an adjustment valve is placed in the hose that is supplying pressure to the wastegate diaphragm. With any aftermarket ECU a Boost Control Solenoid is required to do this function, and this solenoid is controlled with a duty (varying 0-100%) pulsed signal.   The purpose of the solenoid is to allow the pressure that is supplied to the diaphragm to be controlled by the ECU by venting some of this pressure.  By lowering the pressure supplied to the diaphragm more boost pressure is required to open the wastegate valve.  In general, as the duty is increased more pressure is vented from the diaphragm and this results in higher boost levels.  

To provide more control over the desired amount of boost pressure the duty signal can be mapped by the ECU.  There are two methods that we use to control the boost with an Elite ECU:  Open Loop and Closed Loop.

Open Loop Boost Control

Open Loop Boost Control simply means that the ECU provides an amount of duty cycle from a table. The ECU itself does not vary the amount in any way, it simply pulses the solenoid at the duty that the tuner provides.

Closed Loop Boost Control

Closed Loop Boost Control means there is a Target Boost pressure that is trying to be reached, and the ECU can vary the amount of duty based on whether the actual boost pressure is above or below the Target.  This is the point where many believe magic happens and many users have difficulty in understanding how to set it up. In reality there is a logic behind the process that the ECU follows when it makes adjustments and understanding what all of the setting are in the system for is the key to getting the desired result.  As such the next section will cover what the settings all do with much of this explained in the Help section of ESP.

Configuration - Boost Control Tab

Typical Values

Open Loop

Closed Loop

Select whether to use Open Loop or Closed Loop for the control method. The difference is described above.
Tuners discretion. For this guide we are focusing on Closed Loop operation.
Controlled Parameter

Manifold Pressure

Wastegate Pressure

Select whether to use Manifold Pressure or Wastegate Pressure. Manifold Pressure is used for most vehicles where the boost will be referenced from the same MAP sensor used for fuel and ignition control. Wastegate Pressure is used for CO2 two-solenoid control systems.
Manifold Pressure for the sake of this guide

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