Taken from a topic i wrote in the technical essays room:


What Are Air Injectors?
Air injectors, are, as they sound, a set of injectors that inject air instead of fuel. They are commonly used to control the boost pressure output by a turbocharger.

What do they look like?
There are various types available, but the most common ones are as follows.

There are however many types available nowadays, including ones that only run a single injector.

How do they work?
The air injectors have an input to the top of them from the turbocharger and an output on the bottom to the wastegate. The injectors are wired to the ecu so they can be controlled.

The ecu air injector map is mapped against boost, rpm and air temperature. The injectors initially stay closed, keeping the wastegate closed too, encouraging the turbo to spin to speed as fast as possible. When the desired turbocharger pressure is aquired during mapping, the injectors are pulsed so that they open at that point, allowing air to flow to the wastegate. This of course opens the gate, bypassing some exhaust gas from the turbine wheel, slowing the compressor and leveling or dropping the boost pressure depending entirely of course on how much air we allow through. The beauty of this system is we can use a relatively weak actuator to achieve very large boost levels and we can accurately program boost curves into the system.

Any downsides?
Yes, if the injectors fail, due to the “Bleed On” configuration, the turbo will run whatever boost it can until something either stops it or something fails due to the fact we have blocked the pipe to the actuator.