Actual stringent regulations on emission level imply highly efficient control strategies, which can be based on the instantaneous engine torque or the in-cylinder pressure. To reach this objective, while avoiding costly direct measurements, the estimation of one of these variables is required. In this paper, two methods are presented based on the correlation between the crankshaft velocity and the indicated torque or pressure. In the “mechanistic method”, the model based on the dynamics of the reciprocating engine and on a correlation with the combustion process provides a relationship between the fluctuating component of the instantaneous crankshaft acceleration and the average indicated torque of the firing cylinders. Thus, an indicated torque signature of each cylinder can be estimated from the observation of the crankshaft acceleration. In the “stochastic method”, all the complexities of the actual physical system are self extracted in the form of second - or higher - order correlation functions between the pressure and flywheel measurements. Once appropriate coefficients are determined from these functions, the estimation amounts in the evaluation of a multivariate polynomial form based on the measurements. These two methods are applied to a multi-cylinder engine. Results are compared and discussed.