This paper presents the results of several studies, performed on different powertrain configurations, aimed at analyzing the correlations existing between torque and speed frequency components in an internal combustion engine. Engine speed fluctuations depend in fact on torque delivered by each cylinder, therefore it is easy to understand how these two quantities are directly connected.The presented methodology allows identifying a dynamic model, expressed as a transfer function that depends only on the structure of the engine-driveline system. The identified model can be used to obtain information about torque delivered by the engine and combustion positioning within the engine cycle starting from engine speed measurement. The speed signal is picked up directly from the sensor facing the toothed wheel that is already mounted on the engine for control purposes.This is a methodological approach, therefore it can be applied to engines with different powertrain configurations, both Compression Ignition and Spark Ignition.In order to clarify all the critical aspects related to the application of the methodology, this work reports the results obtained applying it to 5 different engine - driveline configurations. Many tests were performed both on Compression Ignition and Spark Ignition engines, taking also into account one case in which combustions are not evenly spaced. After having evaluated indicated torque and its harmonic components from in-cylinder pressure signals, it was possible to identify the relationship between torque and speed frequency components for all the analyzed configurations. Influence of the type of combustion performed has been discussed, as well as the effects related to cylinder filling and firing sequence.