A method for reducing the range of fluctuation of the exhaust emission values of identically constructed engine arrangements of a production series, each having an internal combustion engine and an exhaust after treatment system. After manufacturing identically constructed engines, their engine controls are placed into a calibration operating mode and the engines are operated in calibration operating mode. At least one exhaust gas state variable is recorded along the exhaust gas flow and the measurement value is compared with a desired value or desired value range defined for the production series. If necessary, at least one setting variable of the respective engine is adjusted so that the actual value corresponds to the desired value or lies in the desired value range. Then the calibration operating mode stopped, the engine controls are put into a normal operating mode, and the internal combustion engines are operated in the normal operating mode.