text: the power stroke. As such, BMEP is a con- 
  venient index for a majority of items of recip- 
  rocating engine output, efficiency, and operat- 
  ing limitations. 
  
  of friction and the mechanical output is less 
  than the available pressure energy. The power 
  output from the engine will be determined by 
  the magnitude and rate of the power impulses. 
  In order to determine the power output of the 
  reciprocating engine, a brake or load device is 
  attached to the output shaft and the operating 
  characteristics are determined. Hence, the 
  horsepower, BHP, is used to 
  term “brake” 
  denote the output power of the powerplant. 
  From the physical definition of “power” and 
  the particular unit of “horsepower” 
  (1 h.p. = 
  33,ooO ft.-lbs. per min.), the brake horsepower 
  can be expressed in the following 
  
  The actual power output of any reciptocat- 
  ing engine is a direct function of the combina- 
  tion of engine torque and rotative speed. 
  Thus, output brake horsepower can be related 
  by the combination of BMEP and RPM or 
  torque prc~surc and RPM. No other engine 
  instruments can provide this immediate indi- 
  cation of output power. 
  
  form. 