Commercial Heavy vehicles (CHVs) are an efficient and reliable link between marine, railroad, and air transportation nodes. The vehicle braking power imposes an important constraint in the allowable vehicle speed. The compression brake augments the vehicle retarding power and is currently typically used as an on-off device by experienced drivers. Hardware and software advances allow modulation of the compression brake power through variable valve timing, and thus, enable integration of the compression brake with service brakes. To analyze how much the compression brake affects vehicle speed during braking, we develop a crank angle engine model that describes the intrinsic transient interactions between individual cylinder intake and exhaust gas process, turbocharger dynamics, and vehicle dynamics during combustion and variable brake valve timing. The model is validated using experimental data. Using system identification techniques we develop low-order mean-value models appropriate for control analysis and design.