How this calculator works
Brake work delivered over a cycle equals crankshaft torque multiplied by the angle turned during that cycle. Dividing this work by total swept displacement gives BMEP. A four-stroke engine uses two crank revolutions per cycle, while a two-stroke uses one. Use torque measured at the crankshaft; wheel torque includes gearing and losses. BMEP is not the peak combustion pressure.
Formula
BMEP = 2 pi r T / V; T = BMEP V / (2 pi r), where r is crank revolutions per cycle.
Worked example
A four-stroke engine producing 100 N m from 2 L has BMEP 628318.531 Pa, about 6.28 bar. A two-stroke producing the same torque from 1 L has the same BMEP.
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Frequently asked questions
Does RPM enter the equation?
Not when torque is known. RPM is needed to convert measured brake power to torque.
Is BMEP a cylinder pressure reading?
No. It is a hypothetical constant pressure that would give the measured cycle work.
Which displacement belongs here?
Enter the sum of swept volumes for all cylinders, excluding clearance volume.