Tier 4 emissions legislation is emerging as a clear pre-cursor for widespread adoption of exhaust aftertreatment in off-highway applications. Large bore engine manufacturers are faced with the significant challenge of packaging a multitude of catalyst technologies in essentially the same design envelope as their pre-Tier 4 manifestations, while contending with the fuel consumption consequences of the increased back pressure, as well as the incremental cost and weight associated with the aftertreatment equipment.This paper discusses the use of robust metallic catalysts upstream of the exhaust gas turbine, as an effective means to reduce catalyst volume and hence the weight and cost of the entire aftertreatment package. The primarily steady-state operation of many large bore engine applications reduces the complication of overcoming pre-turbine catalyst thermal inertia under transient operation. Upstream placement of the catalyst packages also offers potential for reducing the overall fuel consumption penalty (associated with the use of aftertreatment) in comparison to the conventional post-turbine placement. This softening of the fuel consumption penalty can be attributed to better light-off and performance of catalyst substrates, as well as a reduction in the impact of aftertreatment pressure drop on engine pumping work.The investigation involved numerical simulation of pre-turbo application of a diesel oxidation catalyst (DOC), partial-flow diesel particulate filter (DPF), and selective catalytic reduction (SCR) catalyst on a 30-35L class diesel engine. The effect of this placement over traditional downstream placement in terms of fuel consumption, package size, weight and cost was examined.The investigation revealed that the inherently higher gas density in the pre-turbine location allows a dramatic reduction in catalyst volume of up to 70%. The fuel consumption penalty associated with the addition of aftertreatment can also be reduced by approximately 1% with upstream placement of the catalyst packages.