Abundant supply of Natural Gas (NG) is U.S. and cost-advantage compared to diesel provides impetus for engineers to use alternative gaseous fuels in existing engines. Dual-fuel natural gas engines preserve diesel thermal efficiencies and reduce fuel cost without imposing consumer range anxiety. Increased complexity poses several challenges, including the transient response of an engine with direct injection of diesel fuel and injection of Compressed Natural Gas (CNG) upstream of the intake manifold. A 1-D simulation of a Cummins ISX heavy duty, dual-fuel, natural gas-diesel engine is developed in the GT-Power environment to study and improve transient response. The simulated Variable Geometry Turbine (VGT)behavior, intake and exhaust geometry, valve timings and injector models are validated through experimental results. A triple Wiebe combustion model is applied to characterize experimental combustion results for both diesel and dual-fuel operation. The ignition delay and injection timing are determined through an iterative calculation based on Start of Combustion (SOC) and a predictive ignition delay correlation. The simulation was subsequently utilized to characterize power delivery delays experienced by the driver during transient tip-in/tip-out conditions. Simulation was able to trace the experimentally observed trajectory, and the transport delay of the natural gas charge induction was identified as the root cause. The insight enabled dynamic adjustment of the diesel injection quantity to compensate for the natural gas induction delay. The diesel compensation algorithm was finally validated throughout the operating range.