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I know the original topic is a bit old now, but the top curve represented the wide open throttle torque, and each of the islands represents different part open throttle curves shown in contour format which is a way of referencing 3 dimensional data in a simplified two dimensional format.
The BMEP is a function of the work done per cycle divided by the displacement volume of the engine, and is a way of converting power in Kilowatts into the non displacement dependent variable of pressures which in an ideal engine would scale perfectly without regard to displacement.
The reason BMEP and Torque are sometimes interchanged the labled axis of the BSFC charts has to do with the fact that BMEP can be derived from the equation 2*Pi*Torque*Z / Displacement volume (for metric units in N-m for torque, and meters cubed for displacement) (Z=2 for four stroke engines and 1 for 2 stroke engines) BMEP can also be described as normalized torque.
Brake specific fuel consumption is based on the mass flowrate of the fuel divided by the power output of the engine in metric that becomes grams per kilowatt-hr.
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