Pre-turbo aftertreatment systems benefit from an increase of the temperature across the monolith reducing the time up to DOC light-off and reaching better conditions for passive regeneration in the DPF. The engine performance is also improved by reducing the specific fuel consumption. The pumping work diminishes because of the lower aftertreatment pressure drop due to the higher gas density. Additionally, the aftertreatment pressure drop is not multiplied by the turbine expansion ratio to set the engine back-pressure, which becomes lower. It also makes the DPF pressure drop less dependent on the soot mass loading. In this context, the traditional ratio between engine displacement and DOC & DPF volume in post-turbo aftertreatment placement needs to be reviewed in pre-turbo applications as a way to optimize savings in fuel consumption and aftertreatment manufacturing cost.The effects on engine performance of the DOC and DPF macro-and meso-structure have been compared with results of standard post-turbo aftertreatment location. The work is performed by modeling based on experimental data of post-and pre-turbo aftertreatment configurations in a diesel engine. A reduction in aftertreatment volume close to 50% has been found attainable preserving its performance and without negative effect on fuel consumption. An optimization of the DPF cellular size has been also conducted to reduce further the pressure drop under soot loading conditions for every volume without affecting filtration area, open frontal area fraction and mechanical and thermal integrity. Finally, the advantage that the aftertreatment volume reduction brings is assessed in terms of the effect on the engine transient response under cold wall conditions.