The small hole to the left of the turbine is the internal wastegate valve. These internal
One hundred twenty six full throttle dyno pulls. We're pretty sure Jesse Rodriguez of Diamond Star Specialties had no idea what he was getting into when he volunteered his car for our boost controller test. Amazingly, the only problem we had was paint melting off his rear bumper.
For such a seemingly simple device, boost controllers vary wildly in cost and complexity. Electronic boost controllers offer in-cabin adjustability, supposedly better boost response and advanced mapping capabilities, but some claim mechanical systems work equally well at a fraction of the cost.
In an effort to learn the real difference between $50, $250 and $750 boost controllers, we ran all the controllers we could find on Rodriguez's very angry Eclipse GS-T Spyder.
Boost Control Basics
Every modern turbocharger uses a wastegate to regulate boost. The wastegate is simply a valve that allows exhaust to bypass the turbine, limiting the energy available to drive it . When designed into the turbine housing, they're called internal wastegates, the kind found on nearly all production cars. External wastegates are located separately from the turbocharger, somewhere between the exhaust ports and turbine housing. The remote location allows the valve to be bigger and flow path smoother, resulting in better boost control and the ability to safely manage a more powerful engine.
The wastegate is held shut by a spring, and as boost builds, the wastegate actuator diaphragm pushes the wastegate open against this spring. The size of the diaphragm and strength of the spring determine how much boost it takes to open the wastegate.
All the boost controllers in this test act on the pressure signal that opens the wastegate. Reducing this pressure will keep the wastegate closed, allowing more boost to build. When the desired boost setting is reached, the controller lets pressure into the diaphragm, opening the wastegate.
The gold-colored can is the wastegate actuator. Boost pressure in this can pushes on a dia
Electronic controllers use either stepper motors or solenoids to do this. Stepper motor assemblies vary the opening of a precision valve, similar to a water faucet. This action is accurate, though somewhat slow. Solenoids, however, operate in either a fully open or closed position, but can change this state very quickly, feeding and releasing full pressure so quickly that the pressure in the diaphragm can be accurately controlled. Dual solenoids will give an even greater degree of precision. The HKS EVC EZ, EVC IV, and GReddy PRofec A all use an identical stepper motor assembly. The GReddy PRofec B and Blitz SBC i-D share a common dual solenoid design, though they drive them differently. A'pexi stands alone with its single solenoid design.
If a wastegate is set to 10 psi, it may start to open around 6 psi, slowing the turbo's acceleration and finally reaching equilibrium at 10 psi. Boost controllers can improve turbo response by keeping pressure off the wastegate as long as possible, making more energy available to drive the turbine. Just as boost reaches the set point, pressure is dumped on the diaphragm to rapidly open the wastegate, and hopefully keep from spiking the boost.
By Josh Jacquot
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