That depends on how good you are at working your speed. On flat level ground where the throttle won't be changing at all then there is no advantage to using your foot. On hills where you can speed up a bit going down the hill, and also let off a bit going up the hill then there is something to be gained.


It varies engine to engine. If you can get a dyno graph showing where your engine is making the most power that is where where the engine is most effiecent, but even then it may use more fuel then you want. A dyno sheet will show you at what rpm it starts making power at. Some where between where it stops flat-lining and where peaks out will be best. Kinda vague I know, but if you are trying to keep it below 2000 rpm, and the engine isn't starting to come alive until 2300rpm then you aren't gaining anything. I had a little Dodge car with a V6 that got better mileage in top gear at 75 than at 60 just because it wasn't working in an effecient rpm range.



Automatic transmissions will sometimes make use of the torque converter slipping to keep the engine in the effiecent range. In the case of getting as much power to the ground as possible a little bit of slippage is also good as you get a sort of multiplication in torque because of it slipping. I don't honestly know why, and mechanical engineer could chime in on that. There is a very fine line where that actually works though. Honda probably spent a fair amount of effort to keep it in that rpm range and that is why it is shifting. Nowdays the valve bodies are all controlled by the computer.

Get a graph showing at what rpm your engine is making HP/TQ at. There is also a diminishing return where the engine may be making better use of the fuel, but you are pushing so much air that it negates the gain in efficiency. My diesel pickup gets stupid good mileage at 1200 rpm, but I'm only doing less than 40mph in 6th gear.