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Internal and external wastegate


Information about wastegate

  1. Wastegate, what is it?
  2. How does a wastegate work?
  3. Why is wastegate used?
  4. Connections
  5. Different types of wastegate
  6. Internal or external?
  7. Choice of size
  8. Installation
  9. Basic charge pressure
  10. Adjust wastegate spring to max boost pressure
  11. Material
  12. Accessories
  13. Check your wastegate
  14. Problems
  15. Compare wastegate


Wastegate, what is it?

The wastegate is a valve that controls the charge pressure of the turbocharger using vacuum and pressure.

A Wastegate is a device that helps control the boost pressure in a turbocharged engine—regulating the exhaust gases flowing through the turbo and limiting the maximum amount of boost pressure produced. This helps prevent excessive boost pressure and keeps the turbo running for the best performance.

Wastegate valves usually consist of one inlet and one outlet that is opened and closed using a charge pressure control valve. The charge pressure valve is connected to the wastegate valve and is responsible for opening and closing it. The boost pressure control/boost pressure valve opens and closes the wastegate to regulate how much exhaust gases flow through the turbo and, thus, how much boost pressure is produced.

The external wastegate is essential in performance applications and helps to adjust the boost pressure and keep the turbo running. Without a wastegate, an engine can be damaged by too high charge pressure, and the pressure pulses can damage the turbo. So if you are considering fitting a turbocharger, include an external wastegate.


How does a wastegate work?

A wastegate lets part of the exhaust gases through before they reach the turbine of the turbocharger in order to relieve the turbo from giving an unwanted boost pressure. The exhaust gases are released through the Wastegate's vavlve, which then leads out to the exhaust system. In performance applications, this is sometimes led directly into the air so that turbulence is not created in the exhaust system.



Why is wastegate used?

A Wastegate is used to regulate the charge pressure so that the desired charge pressure is maintained and to counteract an unwanted peak charge pressure.

An external wastegate is usually needed when the internal wastegate in the turbo cannot control boost pressure effectively enough. This can happen for a number of reasons, including a faulty or damaged internal wastegate, an incorrect wastegate spring size, or simply because the boost pressure is too high / flow is to high / backpressure to high for the internal wastegate to handle. Whatever the reason, an external wastegate can help regulate boost pressure and prevent the turbo from over-revving.

A wastegate can also be used to fine-tune pressure levels. By adjusting the position of the external wastegate releaf pipe, it is possible to change how much exhaust gas is directed away from the turbine wheel. This can be used to increase or decrease boost pressure as needed, allowing for more precise control of the turbo's output / boost pressure.




  • Exhaust inlet

The exhaust inlet is where the engine's exhaust gases enter the exhaust valve on the external wastegate. An internal wastegate is located in the exhaust housing of a turbo so the inlet is the part of the turbine housing where exhaust gases can reach the internal wastegate valve. Connections on the external wastegate are usually v-band or a bolted flanges.

  • Exhaust outlet

Exhaust outlet is where exhaust gase are evacuated. This applies to both internal and external wastegates. This is connected to the engine exhaust system, after the turbocharger turbine wheel. The external wastegate, on the other hand, can also direct the exhaust gas directly into the air and not back into the exhaust system. Connections on the external wastegate are usually v-band or a bolted flanges.

  • Vacuum

Connect to the engine vacuum via the engine intake manifold, vacuum station. Some wastegates are prepared for back pressure controlled valves and can then have two vacuum connections. One connection above the wastegate membrane and one below the membrane. Connections are usually a threaded female with 1/8" NPT.

  • Water in / out (wg cooling)

Some wastegates have water cooling connections. These do not need to be connected in a certain flow. Connections are usually a threaded female with 1/8" NPT.



Different types of wastegate

There are actually two options of Wastegates, one is internal and built into the turbine housing of the turbo. The other variant is external and is mounted on the exhaust manifold.

Both are adjusted via the boost pressure valve that is connected to a ECU. pressure is regulated to the desired boost pressure, and how much the valve is kept open or closed.



Internal or external?

To make the choice of external vs. internal wastegate easier, we will address factors that influence the choice.


One factor in choosing an internal over an external wastegate can be lack of space and the external wastegate cannot be used. Another factor may be how service-friendly it should be. The internal wastegate is often very easy to work with as there are minimal extra parts to consider.

On the other hand, there can sometimes be such a tight space around the turbocharger that the external wastegate must be used.

Flow / Power

Although an internal wastegate can handle power up to 1000hp (in some cases), it is more common to use the external wastegate for power outputs over 5-700hp. They are available in a variety of sizes and designs to suit most needs. You can even use two external valves to get extreme control over the boost pressure.

Despite this, an internal wastegate is an alternative that can be used. But then it is important that factors such as exhaust back pressure in the front exhaust pipe / Downpipe are significantly lower than the manifold pressure so that the wastegate can really evacuate exhaust gases properly and achieve its full potential.



Choice of size

Which size of wastegate should be used depends on many factors, including the engine's displacement, type of fuel used, available space for the wastegate (and position/angle), maximum engine speed, number of turbo units, number of wastegates used and desired boost pressure / boost pressure range.

Some general guidelines to facilitate wastegate selection:
• Large turbo / low boost pressure = Larger Wastegate.
• Large turbo / high charge pressure = Small Wastegate.
• Small turbo / high boost pressure = Small Wastegate.
• Small turbo / low boost pressure = Larger Wastegate.




In the perfect world for the wastegate, then you should imitate a highway exit. In other words, exhaust gases coming from the engine towards the turbo must smoothly be directed off the path, towards the wastegate. Then you can have a small wastegate and do not have to compensate with the size of the wastegate because of the good flow.

But then it is no longer ideal for the turbo as there is a large surface in the collector which creates turbulence and disturbs the flow. Here you have to compromise.

Then you mount the pipe to the wastegate with a slightly sharper angle towards 90 degrees instead and compensate with a larger size of the wastegate. Then you get a smaller connection surface to the collector despite a larger wastegate. This setup does not disturb the flow to the turbo as much when not in use and can still evacuate enough air

However, you should never angle the wastegate pipe in the opposite direction of the exhaust gases (over 90 degrees). Then you get poor flow to the turbo and wastegate.


A good illustration from Turbosmart showing how to install a wastegate correctly. The picture also show how not to do it.



Basic charge pressure

The wastegate spring installed is the lowest boost pressure you can have. In other words: If a wastegate spring with 7psi (0.5bar) is installed, you cannot have a maximum charging pressure below 7psi.

Without a charge pressure control / charge pressure valve / wastegate valve / wastegate control, you will only achieve so-called base charge pressure.

In addition to spring pressure, exhaust gas pulses and flow can affect when the spring opens or closes.

Basic boost pressure information. (no boost controller installed)

When someone says 1 bar basic boost pressure, it's connected as in the picture. The hose goes from the turbocharger compressor housing to the wastegate. This way, the wastegate spring will define max boost allowed.
1 bar spring will open at 1 bar and 0,5bar open at 0,5bar.
Some things are affecting this from happening.
1. Exhaust backpressure can slightly raise the base pressure
2. Wastegate valve movement affects wastegate control much.
3. Bigger wastegate diaphragm can control pressure better than a small one.
Many more things affect basic boost pressure.

Make sure this work 100% BEFORE connecting a boost controller.


Adjust wastegate spring to max boost pressure

The back pressure at the wastegate valve works against the charge pressure in the intake. 1 bar in the intake resists about 1 bar at the wastegate valve. Also, you have the spring installed to help keep the valve closed. Installed spring of 0.5 bar and charge pressure of 1 bar resists approximately 1.5 bar at the seat of the wastegate valve. But with exhaust gas pulses and flow affecting the pressure in the manifold towards the wastegate valve, so it is not an exact number.

Higher exhaust gas flow can prevent the valve from opening and higher exhaust back pressure can cause the valve to open earlier than 1.5 bar acording to above example.

If the valve opens too early, before the desired maximum charging pressure, a stronger spring can be fitted to withstand the higher pressure. Even the installation / placement of the wastegate changes the pressure at which it opens / closes in relation to the pressure of the spring.




Internal wastegate

An internal wastegate that is mounted on an original car is usually made of a pressed sheet metal construction where the membrane is not replaceable. Should this break, the entire unit will need to be replaced. In the aftermarket, the housing for an internal wastegate is made of milled aluminum which is separable so that the diaphragm can be replaced. Other parts such as the wastegate arm and other mounting details are made of steel.

External wastegate

An external wastegate is often fitted aftermarket and finer materials are used almost exclusively.

The bottom part (the hot side) is cast in aluminium.

The top part (the cold side) is milled in aluminium.

In the same way as an internal wastegate for the aftermarket, the top section can be split and the diaphragm can be replaced as a service part. Accessories are made of steel.




Boost pressure valve

A MAC valve / solenoid valve that is connected between the pressure side of the turbocharger and the wastegate. This unit enables regulation of the charge pressure.

Wastegate diaphragm

The diaphragm is connected to the wastegate valve. When pressure or vacuum builds up, the diaphragm opens or closes the wastegate valve to regulate exhaust flow through the turbo.

Wastegate spring

The spring that keep the wastegate valve closed. The pressure on the wastegate spring is what is called basic charge pressure. Without a boost pressure valve, this pressure will be the max boost pressure.

Wastegate arm

A wastegate arm connect the vacuum side (cold side) to the wastegate valve (hot side) on the turbo exhaust housing. A wastegate arm is only used on internal wastegates. There are straight and curved arms. Always use a straight arm if you can, the chance is greater for good function, even if you can use an angled wastegate arm on an internal wastegate, it is not something we recommend as it can bind more easily because the pulling force is not straight.

Vacuum fittings

Different types of fittings for connecting vacuum. It can suit both silicone hose, PTFE and pneumatic hose, depending on how you want the installation.



Check your wastegate

Check leakage and vacuum

By putting pressure on the upper or lower part of the diaphragm, you can see if there is any leakage before you mount the valve on your engine. When you put pressure on top of the membrane, it should not leak at all, it should be completely tight. Some wastegates are prepared to be used with back pressure for faster / better regulation. Then you can connect pressure on the underside of the membrane. When you pressurize this side, it will leak a little between the valve guide and the valve itself. This leakage is perfectly fine as it does not affect engine function. Suspicion of excessive leakage here must be checked with the workshop / installer, who must then measure this. Generally, the pressure is released in a second or more. If it goes faster, the play may be too large, which indicates wear.

Test movement

By putting pressure on the lower part of the membrane or vacuum on the upper part of the membrane, you can open and close the valve in the wastegate. In this way, you can easily see if the valve moves freely without binding.

Test spring pressure

By putting pressure on the lower part of the membrane or vacuum on the upper part of the membrane, you can see at what pressure the valve opens. This is the pressure of the wastegate spring that is installed.

Note that an installed wastegate also works together with the engine's back pressure and exhaust pulses which means that a 14psi spring does not always open at 14 psi. This is controlled when tuning  the car. Fine-tuning of the spring pressure further can then be done.



A malfunctioning wastegate can cause serious engine damage, as the turbo no longer has boost pressure control. This means that the pressure will continue to build, and the turbine will continue to spin until something breaks or is stopped by safety features in the engine management! In most cases, the best solution is to replace the worn internal parts with new ones.

Simple troubleshooting of the valve is to disconnect the boost pressure control valve and only use basic boost pressure. Step 2 is to dismantle the valve and check according to point 13. Also vacuum leakage through vacuum hoses to and from the wastegate is a major influencing factor.

  • No boost pressure

The valve is open. This is called Boost creep and means that the valve is open. When the wastegate valve is open, little or no charge pressure can build. Depends on the vacuum across the diaphragm or binding valve.

The valve can start to bind when it gets hot and then work well again when it cools down.

  • Uneven boost pressure

This is often due to a troublesome charge pressure control. (Setting in ECU or hardware).

But it can also be due to a binding wastegate valve.

  • Only full boost pressure

The valve is closed. If the valve got stuck in its closed position. It can also be due to incorrect charge pressure control.

If the wastegate is installed wrong, the flow quickly passes past the wastegate. Or if the engine produces a such high flow that the exhaust gases pass by the wastegate, rampant boost pressure/pressure peaks are achieved. This is bad for the engine and must be fixed.