strad wrote:I admit I'm a little confused. I thought BMEP was more of a tuning tool.
It's just a convenient way of expressing the output of the engine. For ease of comparison between dissimilar engines. As it's linked to both power and work output when tuning a specific engine you can use any metric you like.
The MEP curve is the same shape as the torque curve. Becuase:
Pmep = Pn / Vd*N
Where: P is pressure, n is to distingush between 2 and 4 stroke. The N is rngine speed. As engine speed is a multiplier and it changes, the MEP curve is a different shape to the power curve.
It can be expressed as torque:
Pmep = 2pi*Tn / V.
As you can see the 2 pi and n are constant, and the Volume displaced by the engine is constant. So
Pmep ~ T. (MEP is propoertional to torque).
When not comparing engines, it's more straight forward to talk about torque output as they physical output. Or power output if you want to know what the engine is capable of.
Before you said, why don't be stick with the real world. Engineering is all about making assumptions, that still reflect reality but reduce complexity. So as much as we deal with real issues, we try to make them as close to the theoretical ideal as we can (makes the analysis and maths easier).
The bottom line for tuning (ignoring things like mixtue quality), is simply to cram as much air in as possible. It doesn't matter what figure you use to measure the output, the goal is always the same.