text: TN 
  
  BHP= 5255 
  
  where 
  
  BHP= brake horsepower 
  
  T=output 
  N=output shaft speed, RPM 
  
  torque, ft.-lbs. 
  
  In this relationship, 
  the output power is ap- 
  preciated as some direct variable of torque, T, 
  and RPM. Of course, the output torque is 
  some function of the combustion gas pressure 
  during the power stroke. Thus, it is helpful 
  to consider the mean effective gas pressure 
  during the power stroke, the “brake mean 
  effective pressure” or BMEP. With use of 
  this term, the BHP can be expressed in the 
  following form. 
  
  BHP=@MEP)(D)(N) 
  792,m 
  
  where 
  
  BHP= brake horsepower 
  
  BMEP= brake mean effective pressure, psi 
  D=engine displacement, cu. in. 
  N= engine speed, RPM 
  
  the 
  The BMEP is not actual pressure within 
  cylinder, but an effective pressure representing 
  the mean gas load acting on the piston during 
  
  137 