Current energy and environmental situations have been driving the development of new alternative energies, especially in transportation sector. The objective of this research is to present a decision support methodology to compare engine torques between using the average value and the new approach called response surface. This research investigates the engine torques from neat diesel fuel (WPO (waste plastic pyrolysis oil) 0%) and blend 25% of waste plastic pyrolysis oil by volume in diesel (WPO 25%) at wide range of engine load (20%, 40%, 60%, and 100%) and speed (800 rpm, 1200 rpm, 1500 rpm, 1800 rpm, and 2000 rpm). A heavy-duty multi-cylinder diesel engine was installed on an engine dynamometer and the torque data were recorded. The contribution of this research is to present a more accurate methodology to perform an engine torque comparison. The value of this research lies in the development of a new approach, which is applicable to decision makers in obtaining an engine torque comparison. Consequently, the benefit of the research is that the empirical data from a heavy-duty diesel engine fueled with waste plastic oil blends are revealed. The number of experimentations can be reduced and this leads to lower costs and less time usage for future research. (C) 2015 Elsevier Ltd. All rights reserved.