Turbocharger inlet pressures

In Figure 2 you can see that from position 1 to 2 the piston moves down the cylinder on the intake stroke as it is filled with turbocharger boost air higher than atmospheric pressure, as indicated in line PI. Depending on the valve timing, actual inlet valve closure will control the degree of trapped cylinder air... 

The power output of the Otto cycle can be increased by turbocharging the air before it enters the cylinder in the Otto engine. Since the inlet air density is increased due to higher inlet air pressure, the mass of air in the cylinder is increased. Turbocharging raises the inlet air pressure of the engine above atmospheric and raises the power output of the engine, but it may not improve the efficiency of the cycle. A schematic... 

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