What is the Mean Effective Pressure (MEP) of an engine ?

The Mean Effective Pressure (MEP) is a theoretical parameter used to measure the performance of an internal combustion engine (ICE). Even if it contains the word “pressure” it’s not an actual pressure measurements within the engine cylinder.

The cylinder pressure in an ICE is continuously changing during the combustion cycle. For a better understanding of the pressure variation within the cylinder, read the article The pressure-volume (pV) diagram and how work is produced in an ICE.

The mean effective pressure can be regarded as an average pressure in the cylinder for a complete engine cycle. By definition, mean effective pressure is the ratio between the work and engine displacement: