1. A method for adaptation of transient engine performance comprising the steps of: conducting transient testing, during which an engine is operated in a transient state by making changes to control values of controlled factors supplied to the engine and its output is captured; capturing engine output data produced by the transient testing and creating a transient model of the tested engine based on the relationship between the output data and data concerning the supplied controlled factors; obtaining control values of controlled factors that satisfy transient performance objectives required of said engine, using the transient model that has been created; confirming whether the required transient performance objectives are satisfied by conducting transient testing by supplying the control values obtained from the transient model to the real engine; and creating control software for a control circuit controlling the engine if the confirmation step finds that the required transient performance objectives are satisfied.