Any vehicle with a turbocharged engine needs a wastegate. This valve is an essential component because it diverts exhaust gasses away from the engine and helps control the "boost" that turbocharged engines are supposed to give. Vehicle owners who need to upgrade, rebuild, replace, or repair their wastegate must understand a few facts about this essential part, ranging from the different types available to the proper way to determine the correct size.
Although the function of a wastegate is relatively easy to understand, the way in which it accomplishes this process is more complex. There is a device within a turbocharged engine called a pressure actuator. Controlled by the manifold pressure within the engine, there is a spring inside the actuator that holds the valve of the wastegate closed most of the time. As pressure builds, the actuator progressively opens the wastegate to allow exhaust to escape and bypass the engine turbine. This, in turn, regulates the manifold boost pressure and maximises the performance of the turbocharger.
Types of wastegates
Whilst the function of a wastegate remains unchanged regardless of its type, there are two specific wastegate styles, which impact what buyers need and how repairs to the wastegate are made. There are also specific advantages of each type of wastegate that buyers should note.
An internal wastegate is actually built into the turbine housing of the turbocharger. These generally consist of four parts: a flapper valve, rod end, crank arm, and pneumatic actuator.
The advantages of an internal wastegate include a more simple installation process and a more compact final product. When using an internal wastegate system, exhaust gases automatically follow a path that leads back to the catalytic converter and larger exhaust system. For these reasons, most OEM wategate systems are internal.
The external wastegate system is, as its name implies, an addition to the regular turbocharger. These pieces connect outside of the turbocharger itself, usually to the plumbing of the exhaust manifold. In order to use an external wastegate system, there must be a dedicated runner from within the turbocharger that leads to the wastegate.
Generally an aftermarket upgrade to a turbocharged system, the main benefit of an external wastegate is its ability to more precisely regulate boost level. This is because the separate structure of the external wastegate allows for the possibility of reintroducing exhaust, and hence pressure, to the turbocharger downstream of the turbine. This improves performance and is the preferred wastegate system on racing vehicles.
Common wastegate sizing myths
Aside from determining whether to use an internal or external wastegate structure, properly sizing a wastegate according to the vehicle and turbocharger's needs is essential. Unfortunately, a few persistent myths surround sizing.
Larger engines need larger wastegates
Although it does seem that bigger engines need bigger wastegates, the reverse is actually true. In fact, wastegate size is inversely proportional to engine size, although there is some independence between engine and wastegate size ratios. The rule of thumb is as follows:
- A low boost with a big engine requires a big wastegate.
- A high boost with a big engine requires a small wastegate.
- A low boost with a small engine requires a big wastegate.
- A high boost with a small engine requires a small wastegate.
Determining size is relative to the engine itself and also to the performance that drivers want to get from it. In addition, it is important to remember that exhaust flow, or the size and potential flow of a wastegate, also affects total engine power.
Larger wastegate diameter leads to better flow
Unlike the issue of matching size to power and boost, the relationship between flow and wastegate size is directly proportional since the valve diameter directly affects flow rate. Nevertheless, there is still some room for differentiation between turbocharged engines and wastegate systems since flow path also has a direct impact on this performance element. Therefore, buyers looking at wastegates with the same or similar diameters also need to pay attention to the balance between the body of the wastegate, its valve, and its spring, all of which impact the flow path.
How to buy a wastegate on eBay
When you shop on eBay, it is easy to buy a new wastegate or find parts for the one you already have. Once you know the size and type you need, simply perform a keyword search using the main search bar. A simple set of keywords, such as "external wastegate", returns a long list of products. Narrow the results according to size, brand, compatibility, and more using the provided filters. It is also easy to find additional turbocharged engine parts using the same search methods.