What is piston displacement?

The volume of air delivered out of the compressor measured per minute in litres per minute for a given pressure

Piston displacement / suction capacity or any other name is based on a recippotating piston compressor is a pure TTHEORTICAL FIGURE based on the bore, stoke and speed of the compressor. 

The fad is actually what comes out of the compressor after all the ineffiecncies are taken into account against a certain pressure. The higher the pressure the lower the free air delivered. 

Use this handy tool to convert Litres Per Min into Cubic Feet Per Minute