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How do wastegate actuators work?

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Help me understand.

In a single port actuator for an internal wastegate, the boost applied to the actuator port keeps the wastegate closed or helps it open?

Follow up question, if no boost line is connected to the single port actuator, what would be the result using a 5psi spring?


Conventional OEM single port, the spring is holding the valve shut, the boost pressure acting on the diaphragm in conjunction with turbine inlet pressure on the exhaust valve open the valve.

Ratio of set pressure to max can vary a lot but most modern aftermarket valves will be in the order of 2.5×set pressure for low-med spring ratings, a lot of OEM arrangements will do in the order of double.

If you go 4 port solenoid or boost on top port with a 3 port you can achieve many times rated pressure depending on the diaphragm to valve area ratio and efficiency of the turbo system in therm of EMP:IMP for target boost.

Thanks Michael!

So using a 3 port boost solenoid, the boost controller is unable to keep the wastegate closed in a single port actuator? Only help it open?

Or does this mean setting the solenoid to max boost is the same as not having a boost feed to the actuator single port?

Yes on most OEM/single port, 100% duty cycle with conventional solenoid plumbing is like leaving the diaphragm to atmosphere and will probably result in something in the order of twice or more spring pressure.

Worth setting your overboost cut out reasonably tight to target if you are messing around and are not confident in your maps/fuel system capacity/mechanical limits of the engine.

Thanks heaps mate! Makes total sense, just needed a clarification. Cheers!