Miller cycle is applied to improve performance and emission characteristics of a gas engine. There are different types of Miller cycle concept utilization through variation of valve timing either by early intake valve closure or late intake valve closure. In this study finite-volume method is used to analyse the performance and emission characteristics of a four-stroke 12-cylinder turbocharged Miller cycle gas engine. Therefore, experimental data are used to calibrate the results derived from 3D combustion simulation and 1D overall engine simulation. The Miller cycle application shows that about 30 CAD (crank angle degrees) advancement of IVC compared with standard cycle reduces emissions such as NOx to half its magnitude. However, a little reduction in power output seems inevitable. Also, compression ratio reduction contributes to almost 15% decrease in maximum in cylinder pressure. Moreover, retardation of IVC simultaneously improves performance and emission characteristics. However, no significant change of in cylinder peak pressure and temperature is seen. (C) 2016 Elsevier Ltd. All rights reserved.