The NVH optimization process of a power train often consists in a target setting for the acoustic power radiation of the engine in free field working conditions (in an anechoic or semi-anechoic room). This method requires the engine to be dismounted from the car and to be measured in an anechoic or semi-anechoic room which is costly and time consuming. Moreover the free-field characterization is not a good predictor of the acoustic behavior of the power train when it is mounted in the engine bay of a car (very reactive field). This paper presents a number of existing methods to determine the acoustic power radiation pattern of the engine mounted in a car using an intensity probe which is based on a pressure sensor and a particle velocity sensor. For the lower frequencies the velocity probe is used, for the higher frequencies both pressure and velocity is used to measure intensity. A new method for the mid-low frequency range is presented. A measurement in a non-anechoic engine test room is done to determine the relation between the particle velocity close to the surface of the engine to the intensity at a certain distance. This relation is used to estimate the intensity at lower frequencies from the surface velocity.