For the automotive industry, where the Internal Combustion Engine (ICE) has had complete dominance, the transition to new powertrains will be challenging. The new powertrain vehicles must be manufactured with the same efficiency as ICE vehicles in order to reach a competitive price. This article explores some of the manufacturing challenges related to workload differences in current products and those associated with the introduction of new powertrain vehicles in a Mixed Model Assembly line for ICE vehicles. Three possible solutions to workload differences are described in theory, including how they are used in the current manufacturing system and how they might be used when introducing new powertrain vehicles. The solutions found were sequencing, dedicated assembly stations and modularity. In conclusion, it is suggested that modularity is the most efficient method in terms of flexibility and utilization, and some design approaches to facilitate efficient manufacturing are also suggested.