Virtual modeling of engine and predicting the performance and emissions is now becoming an essential step in engine development for off-road application due to the flexibility in tuning of the combustion parameters and requirement of shorter development times. This paper presents an approach where the test bed calibration time is reduced using virtual techniques, such as 1D thermodynamic simulation and 3D CFD combustion simulation for 4 cylinders TCIC engine complying with Stage IIIA emission norms. 1D thermodynamic simulation has played an important role in the early stage development of an engine for selection of engine sub systems like turbocharger, manifolds, EGR system, valve timings etc. The application of 1D Simulation tool for combustion system development, focusing on NOx emissions for an off road multicylinder mechanical injection diesel engine is discussed. The calibrated model, sensitive to parameters like injection pressures, rate of injection, duration of injection, EGR rate, and compression ratio is developed. The boundary conditions like port pressures and temperatures required for 3D CFD simulation are derived from 1D simulation. A commercial 3D Combustion Simulation tool has potential capabilities in modeling in-cylinder combustion to predict the performance and emissions. Various approaches and strategies performed to develop a family of engines with the assistance of simulations is also discussed. After validating the benchmark engine for the selected load points, combustion simulation has been carried out extensively considering various design parameters like ports, manifolds, bowl shape, EGR and injector parameters, and their interaction effects. Detailed analysis on the dependency of parameters on emission and performance consequently helped in shortlisting the combustion recipe with simulation alone. The hardware selected with above simulation strategies was implemented on proto engine. Initial results indicated a close matching of performance and emission parameters with that predicted from simulation. This has resulted in minimizing efforts and test bed time required for combustion optimization.