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.
A small turbo run at high boost also needs a small wastegate, while a small turbo run at low boost needs a bigger wastegate. That said, the engine configuration will play a significant role in deciding what size wastegate to use, and there are a few applications that require larger gates simply due to their design and exhaust flow.
Honda S turbo conversions, for example, are quite popular, and due to the design of the F-series motor and its high rpm capabilities, we always recommend a minimum of a 45mm wastegate. Rotary engines generate a tremendous amount of exhaust energy and heat, so for those applications, the Progate 50mm and Powergate 60mm are what we would recommend until you go past the plus-psi boost range, at which point you can scale back down to a 45mm or pair of mm gates and still maintain control.
The mounting position of your wastegate is largely determined by your turbo and manifold setup and may be constrained by space restrictions in your engine bay. Many times, the mounting of the wastegate is the last thing people tackle and space constraints then force the need for a larger gate due to the less-than-ideal mounting positions. This is a preview of the paper, limited to some initial content.
Full access requires DieselNet subscription. Please log in to view the complete version of this paper. The simplest turbocharger design from a control perspective is one whose turbine and compressor geometry are fixed and that uses no means to control boost pressure.
The boost pressure provided by this type of turbocharger is entirely determined by the engine exhaust flow and the characteristics of the turbocharger. The turbocharger is optimized for a particular operating condition. Then, the exhaust system automatically routes the bypassed exhaust gases to the catalytic converter and tailpipes. In this system, the speed of the turbine wheel determines the diversion of the exhaust gases.
Besides, the wastegate unit reduces the high boost pressure developed by the compressor to the desired level. Thus, it delivers optimum engine performance with controlled peak cylinder pressure. Furthermore, the waste-gate regulates the pressure of the relief valve. It, in turn, limits the boost pressure in the turbocharger system. This is helpful in preventing the engine from potential mechanical damages caused by the high pressure.
Furthermore, the system automatically opens the waste-gate valve when the pressure reaches the pre-set levels.
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