Turbochargers use what are called “wastegates” which can be either internal or external. These control the exhaust gas so that the turbocharger is able to keep up a certain level of boost pressure which is important for overall performance. Internal wastegates have turbine housing with a flapper which is built-in and opens/closes because of an actuator. These internal wastegates are found mostly in vehicles which have a turbocharger straight from the manufacturing factory rather than as an aftermarket addition. When the boost level is adequate it reaches the flapper vents so that the exhaust gasses go through the downpipe and exit properly, all the while trying to maintain a stable boost level so that the turbocharger is able to function normally. Typically actuators in automobiles are controlled a solenoid which works off an electrical boost that is controlled by a series of vacuum lines.
There is a vacuum line which goes from the intake part of the engine or simply the housing for the turbo compressor so it is able to provide the boost pressure for the engine which is running the entire time. Positive pressure is constantly being sent from the line which goes from the engine intake to the very first pot on the solenoid. This positive pressure eventually turns into output pressure which then goes to the actuator. You will find that these actuators are nothing more than a spring-loaded canister with a diaphragm which is regulated by the amount of pressure which comes from the solenoid. Those who are thinking about getting a turbocharger will certainly want to think about the internal workings of them, including the wastegates which are very important in helping them to function.
The boost level is essentially determined by the spring which is in the actuator when the solenoid has been completely disconnected. The lowest boost setting which a turbocharger can be run on is called the “base boost” and it can easily be raised by simply placing a spring that is slightly stiffer in the canister and you will find it is often necessary for vehicles which have been modified in some way to run higher than what they were originally intended to. The more you know about these internal wastegates, the better you will be at diagnosing problems with your own vehicle. There are a lot of people who rely solely on mechanics to work on their setup, but something the person who put it together should be the one to look and it and fix it.
With external wastegates you will find that they are completely separate from the turbo housing. This type of set up does not rely on an actuator in order to function and instead uses a valve which somewhat resembles those which are used in cylinder heads. All of the exhaust in this setup is diverted directly from the turbo to the exhaust or it simply goes into the outside atmosphere. When it does not divert into the exhaust but rather goes into the outside environment, it is commonly referred to as “divorced exhaust” and tends to be much louder than if it simply diverted to the exhaust. External wastegates have to be put in with a unique type of manifold which comes with an additional runner which will only work with the wastegate itself. With external wastegates there are not as many restrain so they can be significantly larger in size and able to regulate the boost levels more accurately.
If you are thinking about getting a turbocharger in your vehicle, it will be important to know about wastegate maintenance, because it will eventually become an issue which you will have to deal with. Internal wastegates can be quite troublesome because of the fact that the flapper tends to get stuck quite a bit or will not swing as it should. Inspecting the internal wastegate on a regular basis is certainly important if you want to keep it at maximum performance. A stuck flapper can easily result in a lag when it comes to building up the boost levels, so you will need to check it regularly. Those who experience this problem will be able to use something called heat riser lube which is made by GM and will be able to help with keeping the flapper from getting stuck and inhibiting boost. You will also need to regularly inspect the vacuum lines; depending on how old the vehicle is that you are driving or what the overall condition of it is like.