One potential cause of vibration and noise in an automobile results from rotational irregularities of the engine due to changes in the torque which can be alternatively resistive and active during an engine cycle. This paper presents an approach to measure this intracyclic speed phenomena and analyze its influence on the noise behavior of an automobile and its rotating components.The measurement is derived from high frequency sampling of an RPM signal. The influence of the number of teeth, RPM range and sampling methods (fixed frequency versus synchronous sampling) is discussed, highlighting the need for a high sampling rate measurement.The analysis of rotational irregularities are processed by the same order tracking methods as used for vibration and noise order analysis. This permits a single analysis approach to understand the interaction between intra-cyclic speed variations and traditional rotating machinery studies. The use of a sync signal attached to the crank shaft as a data acquisition trigger permits the computation of the variations of the instantaneous RPM with the crank shaft angle. Magnitude and phase variations results can be interpreted by the engine designer based on the knowledge of the kinematics, thermodynamics and aerodynamics of the engine. Magnitude and phase of intra-cyclic RPM change orders can be correlated with the magnitude and phase of noise and vibration orders to study their interdependence.