Manual Boost Controller:
The swing valve assembly in the turbine housing determines how much boost a
turbo will produce. If completely closed, the turbo will spool up to its maximum
pressure. If wide open, the turbo will not boost at all. The swing valve
basically determines how much exhaust gas is retained in or vented out of the turbine
housing. Since we're looking for something in between no boost and full boost, we
need a device to control the swing valve assembly--the wastegate.
The wastegate on my turbo is a Turbonetics
dual port integral unit. It works like this: a line runs from the compressor outlet
to the Pressure Port. This pressure pushes on the diaphragm which in turn pushes the
actuator rod. The actuator rod is connected to swing valve actuator which opens and
closes the swing valve assembly inside the turbine housing.
If the reference port remains open to the atmosphere, the spring inside is the only thing that puts resistance on the diaphragm. The spring is preset to 6psi, but this unit allows you to adjust the spring tension (and thus the set psi) by turning the actuator rod. Keeping the 6psi setting, the pressure will begin pushing the diaphragm and thus opening the swing valve as soon as boost starts. By 6psi of pressure, the valve is as far open as it can be with the spring holding it and boost will not go any higher. You can see the difference between this type of control that bleeds off boost constantly as opposed to an electronic boost controller that will keep the diaphragm closed until 6psi and then open it fully. With the electronic control, you get full spool energy because nothing is bled off until the set boost is reached.
All boost controllers generally all do the
same thing: control the wastegate. The electronic ones are much more accurate, offer
several settings at the touch of a button, and some have Fuzzy Logic that will learn the
boost curve of the turbo on any car. That helps to better control boost drop and
creep. A manual boost controller is basically a proportioning valve that unlike an
electronic one, you have to set by hand. Electronic controllers use stepping motors
that vary the ratio electronically.
As you can see, with a simple proportioning valve, you can add pressure to
the reference port. This, in effect, lessens the pushing strength of the incoming
boost from the compressor outlet and thus does not push the diaphragm as far. In
turn, that doesn't open the swing valve as far open and allows the turbo to spool more.
Pressure to the reference port can be used from the intake manifold or a TEE inline
with the line from the compressor as shown in the diagram above.
This is a photo of my manual boost
controller. In essence, it's a proportioning valve used to regulate pressure to the
reference port on the dual port wastegate. If it was wide open, the same amount of
pressure would be seen on both sides of the diaphragm. In effect, the diaphragm
would not move at all and the wastegate would remain closed. This would allow the
turbo to spool to its maximum pressure and assuredly destroy a rod or two in the process.
Fully closed, it would not add any more pressure to the reference side and the
wastegate would work just as if the reference was open to the atmosphere. So,
somewhere in between is where you want to be. Some patience and an accurate boost
gauge will allow to you test and tune the boost where you want.
Mine is temporarily mounted under the hood due to the amount of vacuum line that I had, however I do plan to move it inside. This isn't a necessarily "set it and forget it" process. Several factors play a role in how much boost your car gets. Weather is the largest factor; barometric pressure, humidity, and most of all temperature, change the density of air. Weather changes take place constantly and thus boost changes constantly. For instance, I set the boost to 9psi and later I when the temperature dropped about 15° I was boosting 10.5psi on the same setting. Thus I needed to adjust it down slightly. Having this inside the car would've meant that I wouldn't have had to find the nearest gas station to pull in and pop the hood. This may sound like a pain, but 9psi is much more fun than 6, so it's worth it!