Worldwide emission regulations are driven the efforts of the automotive industry to meet challenging targets concerning pollution reduction. Nowadays, advances in exhaust aftertreatment systems are primarily required to achieve regulation requirements within the whole engine operating range. Nevertheless, flow parameters, such as the exhaust gas temperature, must be also addressed. This makes engine calibration a fundamental step, but also leads to reconsider the passive design of the exhaust line as a way to improve the engine efficiency. Under this context, a study has been conducted to explore the benefits of heat losses limitation looking for aftertreatment inlet temperature increase at the same time fuel economy is improved. To do so, a baseline diesel engine has been modeled using a gas dynamic software taking special care of the heat transfer processes in the exhaust. The investigation covers the definition of different strategies for exhaust ports and turbine thermal insulation, which are evaluated in a representative range of steady-state operating conditions. As a first step, the theoretical limits and representative technology solutions are considered for each exhaust region. Then, a combination of the most promising strategies has been computed to provide a comprehensive database and analysis of the potential of passive exhaust heat losses control.