There are two curves for a "Taurus like engine" in Appendix A of "Technical Options for Improving the Fuel Economy of U.S. Cars and Light Trucks by 2010–2015" (
http://s3.amazonaws.com/zanran_stora...2470551122.pdf). They are described on page 6 (page 22 of the pdf file):
"Technically inclined readers can see some of the efficiency benefits of our assumed engines by comparing the baseline engine map of Figure A2 with that of the improved engine shown in Figure A3. The top curve of the map represents the peak brake mean effective pressure (bmep, which determines the torque delivered by the engine). The improved design is higher across the board, and notably so at low RPM, which allows
responsive driving in more efficient engine modes. The "island" of minimum brake specific fuel consumption (bsfc, how much fuel is burned per unit of energy output) is not only lower, corresponding to higher peak efficiency, but also covers a broader portion of the map, meaning higher efficiency throughout the driving cycle."
The charts are on pages 74-75 of the pdf file.