Diesel oxidation catalysts and diesel particulate filters are standard aftertreatment systems in Diesel engines which are traditionally placed downstream of the turbine. However, pre-turbo aftertreatment configurations are being approached as a way to improve the aftertreatment performance in terms of light-off and passive regeneration. This exhaust line architecture can also benefit fuel economy. The objective of this work is to analyse experimentally how the pre-turbo aftertreatment placement impacts on the performance of a single stage turbocharged Diesel engine. The work has been divided into two parts focused on steady-state and transient engine operation separately. The first part comprises the analysis of the experimental results corresponding to steady-state operating conditions. The range of operation covers different engine loads and speeds. The engine response with pre-turbo aftertreatment placement is mainly affected by the change in the pumping work caused by the aftertreatment pressure drop reduction and its new location, which avoids the multiplicative effect of the turbine expansion ratio when setting the engine back-pressure. These effects become more significant as the engine load increases benefiting fuel consumption from low to high loads. Concerning aftertreatment performance, the results evidence noticeable benefits in DPF passive regeneration and CO/HC emissions reduction at low engine load. (C) 2014 Elsevier Ltd. All rights reserved.