I know someone already made a post about an Automatic toyota, but here is mine for a mildly modified Subaru impreza 2.5i AWD. I got almost the opposite result as the other member with matrix.
The Test Strip:
565 meters of smooth asphalt track with sunny conditions, 45% relative humidty, 16'c temprature and calm winds.
The car:
2009 Subaru Impreza 2.5i AWD with 89 octane gas, stock internals.
test runs:
multiple runs were done in multiple engine loads. The goal was to achieve 50mph and maintain, then let off at a check point and call mileage at second check point. The runs were timed.
consumption---LOD------RPM
12.7L/100km....95% ....~3500rpm
12.3L/100km....100% ....~4000rpm
11.2L/100km....70% ....~2500rpm
11.0L/100km....95% ....~2500rpm
11/0L/100km....80% ....~2500rpm
10.7L/100km....80% ....~3000rpm
10.7L/100km....70%....~2500rpm
10L L/100km....60% ....~2000rpm
Run....Load(%).....Shifts(RPM)...Consumption(L/100km)...Acceleration Time(s)...
A.........WOT.............5500RPM...........15.8L. 100km
B.......+90%.............3000rpm............13.3L/100km
C.........80%.............2300rpm............12.3L/100km
D.........60%.............1800rpm.............12.1 L/100km
E.........80%.............2300rpm.............12.0
F.........80%.............2500rpm............12L/100km
G.........90%.............3000RPM............11.9L/100km
H.........90%.............3000rpm.............11.9
I..........60%.............1800RPM............11.5 L/100km
J..........60%.............1800rpm.............11. 5
Result:
the above data was used to create this chart:
Conclusion:
Based on the raw data above it seems to me that lower engine RPM along with moderate loads (60%) is essential for optimum fuel efficiency in this car. The lower RPM is understandable due to less fuel enrichment and internal frictions. The reasoning for lower load benefits could be three folds. One it could be due to higher ignition timing at low loads. Higher spark advance improves volumetric efficiency which in turn improves torque and pumping losses. It could also be that rate of acceleration doesn't increase as much when engine load increases pass a certain point. From above chart you can see how steep the engine load incline gets while acceleration rate continues to be steady. So pass a certain engine load the engine is breathing more air yes, it might still be running stoich yes, but it is not producing anymore power to make up for the higher fuel flow. There are also sometimes anomalies such in some low-moderate loads such as temporary lean conditions since most cars are Not equipped with a high-resolution wideband sensor.
^read:
http://download.springer.com/static/...a2357&ext=.pdf