Having found a 1942 (?) copy of
R A Beaumont Aeronautical Engineering: A Practical Guide for Everyone Connected with the Aero Industry (modern reprint
http://www.pitstop.net.au/view/aviat...uery/plu/23199) it's interesting to read what he says about the "four degrees (types) of boost" used by British aero engines:
(1)
Take-off Boost - ...an additional amount of induction-pipe pressure....accompanied by an extra richening of the mixture which prevents an unstable combustion termed
detonation...(p. 105)
(2)
The Rated Boost - often known as maximum climbing boost....boost pressure is reduced to a value which permits the engine to run continuously at that particular power output...(p. 105-106)
(3)
Override Boost - For the greatest possible power output for take-off or emergency, an increase in pressure above the normal take-off boost is permitted on some engines.
This condition is used in conjunction with a special fuel. (p. 106)
(4)
Maximum Cruising Boost....
Thus it is specifically stated that override or emergency boost was used only in conjunction with a fuel that permitted the higher boost rating.