Boost is also the term used for the increase in
intake manifold pressure provided by an operating
turbocharger or
supercharger over
ambient pressure (or original intake pressure). It is expressed in
P.S.I., for
Pounds per Square Inch.
This higher pressure allows the engine to force more air into the cylinders. Of course, this means that more fuel is forced in as well in order to maintain rough stoichiometry.