Diesel engine manufacturers have faced stringent emission regulations for oxides of nitrogen and particulate emissions for the last two decades. The emission challenges have been met with a host of technologies such as turbocharging, exhaust gas recirculation, high- pressure common rail fuel injection systems, diesel aftertreatment devices, and electronic engine controls. The next challenge for diesel engine manufacturers is fuel-economy regulations starting in 2014. As a prelude to this effort the department of energy (DOE) has funded the Supertruck project which intends to demonstrate 50% brake-thermal efficiency on the dynamometer while meeting US 2010 emission norms. In order to simultaneously meet the emission and engine efficiency goals in the cost effective manner engine manufacturer have adopted a systems approach, since individual fuel saving technologies can actually work against each other if fuel economy is not approached from a total vehicle perspective.In this present work an optimization study was undertaken involving combustion improvements, aftertreatment and waste heat recovery technologies. The present paper summarizes experimental results of this effort around two typical driving cycle modal points. The selected engine architecture dictated the technology trade-off between the aftertreatment, combustion and waste recovery approaches. This paper examines the high and low temperature combustion systems associated with the high and low NOx approaches respectively and the engine hardware for each configuration. Combustion improvements in the form of increasing the rail-pressure of injection and waste-heat recovery in the form of electrical turbo-compounding were examined for the high and low-NOx combustion modes.