Simultaneous reduction of NOx and PM from engine exhaust of a diesel engine is an interesting area of research due to the implementation of stringent emission regulations all over the world. Cost involved in expensive after treatment systems such as DPF and SCR necessitate minimization of engine out pollutants. With minimum engine out emission achieved through engine hardware and combustion parameter optimization, possibility of elimination or downsizing of the after treatment system can be explored.The paper presents the effect of fuel injection parameters and EGR rate on exhaust emission of a boosted diesel engine. Effects of parameters such as rail pressure, pilot-post injections, SOI, EGR rate and EGR temperature on a 4 cylinder two valve direct injection diesel engine is studied. Present study reveals the possibility of elimination of after treatment systems at BS IV level with optimization of engine hardware and combustion parameters.A trade off of NOx and PM is observed with variation of most of the combustion and injection parameters. A methodology for arriving at the optimum value of combustion and injection parameters based on NOx-PM trade-off is presented in this paper. Effective pollutant level is calculated by addition of ratio of actual to targeted values of all pollutants. Optimum calibration or combustion settings are arrived at minimum effective pollutant level.