This is very interesting, and if I understand what I'm seeing on these charts, the optimum rpm for fuel economy is slightly lower than peak torque rpm. The fact that the shapes of the curves change at different torque requirements is why modern engines have computers to control them. The computer can make compensations for all the variables. The published torque and power curves are at WOT, but I seldom drive at WOT and don't want to. If I had access to a dyno, I'd like to estimate the power that is required to cruise at 55-60 and then measure fuel consumption at that power level at various engine speeds from about 1800 to 2500 rpm. Once the best fuel economy speed is found for a particular engine at that power level, then find the correct gearing to stay near that speed on the highway. That info may be available but I don't think I've seen it.
