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The common turbocharger wastegate would seem like the height
of simplicity, but high performance can add complications.
By C.J. Baker
Let’s begin by describing
what a turbo wastegate is. A wastegate is essentially a device that bypasses some exhaust
flow around the turbine section of a turbocharger to control maximum boost. A wastegate
is usually controlled by a pressure actuator that is connected to manifold pressure.
The wastegate is normally closed, held shut by a spring inside the actuator canister.
When preset pressure limits are exceeded, the actuator progressively opens the wastegate,
allowing exhaust flow to bypass the turbine, thus regulating manifold boost pressure.
On the surface, it sounds like a simple premise, and in fact, a wastegate is a simple
device. The problem comes from the pressure in the exhaust system, called turbine inlet
pressure that can bear against the valve, overpowering the spring in the actuator, and
forcing the wastegate open at lower than intended boost levels.
Original equipment turbocharger
wastegate actuators are selected or engineered for a specified boost level and turbine
inlet pressure. To keep costs down, such actuators are usually just big enough to do
the job at the stock boost levels. If the turbocharger boost is increased for additional
airflow and performance, the stock wastegate actuator is frequently incapable of holding
the wastegate fully closed until the higher boost level is reached. This happens because
turbine inlet pressure also increases as boost pressure rises. The fix is to use a bigger
spring in the wastegate actuator to hold it closed until the desired peak boost is achieved,
however, that also requires a bigger actuator diaphragm to override the heavier spring
when the desired boost level is reached. That’s why Banks created the Big Head
actuator that’s used on many of its diesel power systems.
The net affect is that
the turbocharger comes up to peak boost more quickly and then maintains that boost level
throughout the engine’s RPM range for optimum mid-range torque and top end performance.
It’s another example of the engineering expertise you get from Gale Banks Engineering.
We do it right.
To look at Banks diesel
power systems that feature the Big Head actuator, click on Power
Systems.
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