Boost Control Explained
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.
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
Setting | Options |
| Typical Values | |
Mode | 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 |
Related Articles
Boost Control User's Guide
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 its namesake, is a gate or valve, that lets waste gases of the engine bypass the turbocharger turbine. If no wastegate ...Boost Control
The Boost Control function is used to regulate boost pressure by controlling the duty of a boost control solenoid. This in turn regulates the air pressure supplied to the wastegate diaphragm. Note: Due to the large number of pressure units, all ...Boost Control Delay
This is the Delay Time between meeting all of the conditions for closed loop, and for it to actually begin correcting the output. This delay is to ensure that the boost pressure has stabilised before trying to making corrections. Typically around .05 ...Boost Control Corrections
Duty Cycle Correction Duty Cycle Overall Correction - When the Mode is set to Closed Loop this will be an overall negative correction to the Base Duty Cycle. When the Mode is set to Open Loop this will be an overall positive or negative correction to ...Boost Control Wiring
Options Output Type One Solenoid - This is the typical setup found on cars which are turbocharged from factory, as well as most after-market turbo suppliers Two Solenoids - This is most typically used when a pressurised gas is used to manipulate ...