Above is a performance map which shows an engine’s BSFC over the entire load
(BMEP) and speed (N) range. A dynamometer is used to calculate brake torque and fuel
flow is entered into the computation to calculate brake specific fuel consumption. This
map only incorporates the wide-open throttle condition, but adding a third independent
axis of throttle position can create a 3D performance map; it is noted that throttling
directly affects efficiency via an inverse proportion, and maximum efficiency and
minimum BSFC is realized at 100% throttle.
BMEP is brake mean effective pressure in the cylinder and is the scale of measurement
for an engine’s potential to produce torque.