Improved blade aerodynamics reduces the number of extra compressor stages required.
Behind the spinner was the intake area and the supersonic compressor stage.
Work continues on a larger version with an additional compressor stage that over doubles the power.
As of the Astazou X, the engine received a second axial compressor stage.
The X and subsequent engines had a second axial compressor stage added.
A third axial compressor stage added for increased pressure ratio.
They increased the air flow through the engine and added a fourth compressor stage (hence the name).
Air is compressed, raising the pressure and temperature, through the compressor stages of the engine.
This air is usually bled off from the engines at the compressor stage.
At the front, where the air is coming in, there is the compressor stage.