Abstract Assembly simulation plays a pivotal role in predicting and optimizing the distortion of an assembly, particularly in the automotive industry where precision and efficiency are paramount. In BIW parts assembly, factors such as clamping, mechanical & thermal joining, and loading direction are important. These factors affect the quality of the final assembly. Predicting and optimizing these parameters in the early design stage can help reduce development time, cost and improve the quality of the final product. Currently, LS-DYNA is used for closures like doors, hoods, and fenders. However, preprocessing, calculation, and post-processing time in LS-DYNA is very high, making it unfeasible for the whole BIW. Employing a comprehensive approach, the authors assess the distortion results, preprocessing, calculation, and post-processing time of both simulation techniques. Notably, the study reveals that AutoForm offers over 50%-time savings across all stages compared to LS-DYNA, without compromising result accuracy. Moreover, AutoForm demonstrates reduced resource utilization and calculation costs, making it a compelling choice for BIW subassembly simulation. This research underscores the importance of early-stage prediction and optimization in reducing development time, cost, and enhancing the quality of automotive assemblies. By leveraging advanced simulation tools like AutoForm, manufacturers can expedite the design process while maintaining stringent quality standards, thus gaining a competitive edge in the market. Keywords: BIW, Assembly Simulation, Distortion Prediction, LS-DYNA, Autoform, Quality Improvement, Simulation Technique