Updated: Oct 16, 2021
An internal wastegate is located inside of the turbocharger housing, it has the advantage of being cheaper and more compact. An external wastegate features a separate pipe on the exhaust manifold leading to the wastegate, it's better for tuning and power.
In this article, I will discuss the various advantages and disadvantages of using a turbocharger with an internal wastegate versus using an external wastegate.
Table of Contents:
What Is a Wastegate?
When it comes to turbocharging, a wastegate is one of those things that everyone has probably heard of, but only a few can describe. Wastegates are basic components of an engine that play an important function in regulating boost levels.
They are surprisingly simple. Because turbochargers operate on exhaust gases, there must be a method to regulate how much exhaust gas is allowed through the turbine of the turbo.
If you add too much, the pressure will surpass acceptable levels, resulting in turbo overheating, engine damage, and a slew of other effects.
A wastegate is what controls the accumulation of boost pressure. When the pressure limit is reached, the wastegate is opened by another component called the actuator, allowing exhaust gases to be redirected, usually back into the exhaust system, bypassing the turbo.
An internal wastegate is an actuator that opens a bypass valve placed within the turbo housing when a certain pressure is reached.
It's small, needs little piping, and since it reroutes unwanted gases back into the exhaust system and the catalytic converter, it's found in almost all OEM applications. It's standard on OEM turbocharged vehicles.
As you can see in the diagram above, the wastegate is located internally within the turbocharger housing, it is controlled via the actuator.
An internal wastegate has several advantages as listed below.
Suitable for OEM vehicles
The internal wastegate is a great solution for affordability and compactness, which is why it is used by essentially all production car manufacturers.
It also has the advantage of using less pipework, making it very easy to reroute into the existing exhaust system, bypassing the turbine, which is great for lowering emissions.
The only noticeable disadvantage is that internal wastegates flow slightly less efficiently than an external waste-gated turbocharger does and they can only deal with limited exhaust gas pressure and flow rates.
The role of an external wastegate is the same, but rather than activating a bypass value inside the turbo, an external wastegate is a completely independent actuator.
An external wastegate allows for rerouting of the exhaust gas wherever desired, the most common being rerouted further down into the exhaust system or directly into the atmosphere, as seen in vehicles with a "screamer pipe".
Further Reading: The Advantages & Disadvantages of a Screamer Pipe
Below are the benefits and drawbacks of an external wastegate system.
External wastegates outperform internal wastegate units in almost every performance metric.
Enhanced exhaust gas and turbo flow
Less back pressure
Improved performance and power potential
Faster turbo spool
Better full-throttle sound (screamer pipe)
The external wastegate is simply a much better flowing system, it allows for higher exhaust gas pressures, increases the rate of spooling, improving power and tuning potential.
If a screamer pipe system is used, it improves the exhaust sound on full-throttle, as shown in the video below.
Of course, there are also drawbacks to an externally waste-gated system. Specifically, a much louder vehicle. However, to some people this is a benefit.
However, if you don't like noisy vehicles, you should avoid this wastegate that vents straight into the environment and instead use an internal wastegate or reroute the exhaust gas back into the exhaust system.
Which One Should You Use?
Is an aftermarket wastegate or turbocharger really necessary and if so, which wastegate should you use?
That is completely dependent on your vehicles boost pressure. If you're running stock boost pressure, the OEM wastegate should be perfectly fine.
As you increase the boost pressure, it will become more difficult for the stock wastegate to accurately regulate boost levels. It makes an aftermarket wastegate a must-have once the boost pressure begins to rise substantially.
This may not be possible on some turbochargers, meaning you may have to replace the turbocharger with a different wastegate setup.
Some aftermarket turbochargers allow you to select whether you want an internally waste-gated turbo or want to use an external wastegate.
For running high power, an external wastegate is better. For stock turbocharger vehicles, and even some hybrid and big turbo vehicles, stock wastegate setups are fine.