text: manifold pressure any greater than the induc- 
  tion system inlet pressure. As altitude 
  is 
  throttle and a governed 
  increased with 
  RPM, 
  the engine is 
  through 
  reduced and BHP decreases. The first forms of 
  supercharging were of relatively low pressure 
  ratio and the added airflow and power could 
  be handled at full throttle within detonation 
  limits. 
  “ground boosted” engine 
  would achieve higher output power at all 
  altitudes but an increase in altitude would 
  produce a decrease in manifold pressure, air- 
  flow, and power output. 
  
  full 
  the airflow 
  
  A change of the blower to a high speed will 
  provide greater supercharging but will require 
  more shaft power and incur a greater tempera- 
  ture rise. Thus, the high blower speed can 
  produce an increase in altitude performance 
  within 
  The vari- 
  ation of BHP with altitude for the blower at 
  high speed shows an increase in critical alti- 
  tude and greater BHP than is obtainable in low 
  blower. Operation below the high blower 
  critical altitude requires some limiting mani- 
  fold pressure to remain within detonation 
  limits. 
  It is apparent that the shift to high 
  blower is not required just past low blower 
  critical altitude but at the point where the 
  transition 
  to 
  from low blower, full 
  high blower, limit hiAP will produce greater 
  the blower speed is 
  BHP. Of course, if 
  increased without 
  throttle 
  the 
  opening, an “overboost” can occur. 