HP vs Torque

["Robert T. Chafin" <rtchafin@xxxxxxxxxxxxxx>]

Andrew T.  writes:
Mark (mjn@domain.elided) writes words to live by:

> At 5252 RPM, no matter what (assuming your engine will rev
> that high), the torque and HP curves must cross and T must
> equal HP.  Period.

This seems a remarkably simple and elegant solution, but totally unlike
most mechanical/kinetic/thermodynamic equations I ever came across at uni.
Is it really that easy, for every engine configuration? And how come 5,252
rpm? Or is that figure derived from an approximation?

Intruiged but confused,

Andrew T
'95 318is.
 
Yes, Andrew, it really is that easy. 
 The figure 5252 comes from miscellaneous conversions, and applies only to
Imperial system measurements;  for example, by definition, 1HP=550 ft-lb
per second (horsepower being the time rate of doing work),  then you
convert (x60) to ft-lb per minute.  Then, 1 revolution is 2pi radians,  so
550 x 60 / (2 x 3.14159...) = 5252
Of course, as others have pointed out, you do have to be mindful of the
scales along the sides of the graphs;  for clarity in interpetation of the
torque and HP curves, the scales are often separated.

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