The Basics– How the Wastegate Works

So, we figured that before we start the boost controller reviews, a little basic info is in order. If you already understand the operation of the wastegate and wastegate actuator, feel free to skip this section. If you are Boosthead Uber-Pro, please chime in on the comments and add your experiences. The more info we can add, the more useful this will be to all the turbo people out there!
Before you can understand which boost controller will be best for you, a basic understanding of the turbo system is in order. The turbo is essentially a supercharger, driven by exhaust gas. The function of any supercharger is to force more air into the system than the engine could draw in from its own pumping action. The air in itself, does not create power. Instead, it allows more fuel to be burned. So, although we all focus on “the boost”, boost alone is not enough. In fact, in the case of the gasoline engine, boost alone can cause a lean condition and destruction of the engine. More on that in a future post.
We’ve mentioned that the turbo is an exhaust driven supercharger. The supercharger is only a type of air compressor, which can be driven by belt, exhaust, electric motor, etc. There are different types of compressors used in supercharger systems, but with turbos, you are essentially dealing with a compressor wheel. This wheel uses an inducer and exducer combination, to pull in air at atmospheric pressure and cram it into your engine. There’s a lot more to this, but this is a “basics” article, so that’s all we need for now.

basic turbo

Connected to the compressor wheel (literally, connected by a shaft), is the exhaust turbine. This is where the “turbo” nickname comes from. Hot exhaust from the engine is directed through the turbine, making it spin. This in turn, makes the compressor side cram more air into the engine, creating “boost” pressure. This allows the engine to:
1) Burn more fuel
2) Make more power
3) Make more exhaust to drive the turbine
If left unchecked, the cycle repeats 1,2,3 1,2,3 1,2,3 until BOOM! Your engine self-destructs. Not the best arrangement, so we need a way to keep the power from climbing, unchecked. Enter the wastegate. The wastegate is a valve (literally, a “gate”) that allows some of the exhaust gas (waste) to bypass the turbine. Now we can add a fourth step:
4) The wastegate opens, allowing the turbine to slow, and the boost pressure (and by extension, the power) to fall. The cycle then repeats.
Connected to the wastegate itself, is the wastegate actuator. This is simply a spring loaded diaphragm that holds the wastegate closed, until a certain boost pressure is reached. Once the boost pressure is sufficient to overcome the spring pressure, the wastegate is opened and the boost pressure falls. The cycle will repeat, if there is sufficient exhaust pressure and boost (i.e., if you keep your foot in it).
This photo shows the actuator, identified by the rubber hose, which carries boost pressure to the diaphragm. From the other side of the actuator “can”, you can see the rod, which connects it to the wastegate. By the way, the shiny side is the compressor side, the brown side is the turbine:


This basic system is all that is needed for the turbo unit to function. The boost pressure will be set to whatever the wastegate actuator spring can support. But of course, we want more boost. So, we must figure out a way to make the boost pressure adjustable. Enter the boost controller. Most factory OEM turbo systems add an electronic boost control system to the equation. These systems are usually not user-adjustable, but they work the same way as aftermarket systems. In the next posts, we’ll explain how electronic and manual boost controllers (MBC) work. Then, we’ll move on to the reviews. We’ve got some cool product lined up and will give you our opinions (good and bad) on these products.

Stay Tuned

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