An engine cycle simulation program has been developed to predict both engine performance and NOx emission with reasonable accuracy. The program is a product that combines two programs, VIPRE™ and ALAMO_ENGINE, both developed at Southwest Research Institute (SwRI). VIPRE™ is a comprehensive tool for engine systems with intake and exhaust dynamics, emphasizing engine performance , while ALAMO_ENGINE is a program focusing on NOx prediction .Demonstrations in this paper were based on a six-cylinder, turbocharged diesel engine with a high-pressure exhaust gas recirculation (EGR) loop. The EGR system is connected upstream of the intake manifold from the exhaust manifold located in the turbine entrance. A two-way butterfly valve is used to control the EGR rate. The major challenge in this modeling work is the prediction of engine performance and NOx emission in an acceptable and systematical fashion. There are many programs used for either engine performance or NOx prediction in literature. [3, 4 and 5] However, very few programs are capable of predicting both engine performance and NOx emission over wide operating conditions with acceptable accuracy. This paper will demonstrate that the program developed by SwRI is one of only a few programs that can carry out this task.Comparisons of engine performance and NOx emission between simulations and measurements were carried out over a wide range of operating conditions. It was shown that the integrated program could predict both engine performance and relative NOx with reasonable accuracy.