The Environmental Protection Agency (EPA) has collected a variety of engine and vehicle test data for use in assessing the effectiveness of new automotive technologies in meeting greenhouse gas (GHG) and criteria emission standards, along with monitoring their behavior in real world operation. EPA’s Advanced Light-Duty Powertrain and Hybrid Analysis (ALPHA) tool was created to estimate GHG emissions from vehicles using various combinations of advanced technologies and has been refined using data from tests conducted at EPA’s National Vehicle and Fuel Emissions Laboratory. This paper describes EPA’s process of constructing full engine maps from engine dynamometer test data for use in ALPHA or other full vehicle simulation models. The paper reviews how EPA uses available data, both steady state and transient, to characterize different operating conditions, and combining them to construct a map suitable for simulation. It examines the calculation of default values, used when specific engine test data is unavailable. Some of the tools used to assess the quality of the generated engine maps before use in simulation are also explored. Another topic examined is the application of the constructed engine maps to different vehicle classes via the scaling of the engine maps incorporating adjustments for heat transfer, friction and sensitivity to knock.