New regulations for vehicles are increasingly demanding on fuel consumption and pollutant emissions reduction. This requires to design new engine concepts and related control strategies. Control design, validation and calibration on test beds is costly and time consuming. To reduce development costs and time-to-market, Electronic Control Units (ECUs) have to be validated at an early stage using a real-time simulation platform based on continuous engine models. To allow real-time simulation of high fidelity engine models, different techniques have to be applied in order to fulfill the real-time constraints. Real-time simulation involves trade-offs between several aspects, such as real-time constraints, models computational complexity and integration accuracy. This paper mainly focus on numerical integration related aspects, by introducing its different methods such as numerical solvers and partitioning=scheduling, and then considering the trade-off between accuracy and simulation speed