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My neighborhood connects to a 4 lane 55 MPH not divided highway.
In eastern Virginia where I live the elevation ranges from 70 feet above sea level to sea level. Elevation changes are small to non existent.
The first 7 miles of my drive has one traffic light and very few intersections or traffic entering or exiting the road.
I found a site where they were dyno testing a 4 cylinder GM engine. At 20 HP load they used 1 unit of fuel. Increasing the load to 50HP the fuel consumed only rose by .5 units.
Basically this demonstrates that the additional 30 HP only cost half as much fuel as the first 20 HP.
20 HP/1 unit of fuel
50HP/1.5 units of fuel
20 HP per unit
versus
33.33 HP per unit
That's the secret of P&G as I understand it.
A hill that was the perfect grade to allow you to use the 33.33 per unit to increase your altitude, then glide down the down slope with the engine off, would give you a huge increase in mileage over driving on a level grade using the 20 per unit rate of consumption.
It would be a short steeper grade then a much longer slighter grade for the coasting portion of the cycle.
I averaged 70.2 MPG in the Insight using the strategy of trying to keep the instant MPG bar as high as I could going uphill, while letting the grade accelerate my car going downhill.
Speed ranged from 65 to 40 MPH. If I remember right the miles were 655 on 9.6 gallons of gas. Average speed on the road was about 55 MPH.
For the last 17k miles on the Insight my average MPG has been 65. That average started in early December so the yearly average will probably be fairly close to 65, maybe slightly less.
On the right heading east are railroad tracks running parallel to the road. On the left is I64 East.
The grades are very small probably around 1% or even less. Elevation changes of 20 feet take several tenths of a mile.
The down slopes are not enough to maintain speed in most cases.
I find that in this specific circumstances my best mileage is to hit my peak speed at the top of the hills and coast as far as possible while maintaining an average of 45 MPH.
Usually this is a range of 52 to 40 MPH.
That gets me 55 MPG in my Echo and almost 90 in my Insight.
The best measurement of load is MAP or a vacuum gauge. Either will tell you how much of the atmospheric pressure is actually getting into the cylinders. Throttle position is not a good measurement as load changes will result in increased MAP (or reduced manifold vacuum).
As you climb a grade and your MAP increases your engine becomes more efficient.
I found that even on flat stretches in the Insight I can accelerate very slowly, about 3-5 seconds per 1 MPH increase, with very little decrease in fuel mileage. This is demonstrates by the instantaneous bar graph in the Insight. If I accelerate about 7-10 MPH at this very gradual rate, then I can let off the throttle and watch the mileage jump to the 100-140 MPG range for about the same amount of time it took to accelerate to the higher speed.
Using this strategy on that 7 mile stretch of road I have seen close to 90 MPG in the Insight.
regards
Mech
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