Speed VS RPM

[BassRanger]

I still feel like I'm missing something. What exactly are you trying to figure out? If it's mpg related, the truck a real time fuel economy gauge. You can compare speeds and see how it effects fuel economy right on the cluster.

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[Muffin1]

Yea what I'm trying to find out (and i guess I'll use the instant fuel gauge like you suggested), but if I'm running at 70 at a whatever rpm, and i push it up what is the crossover over for MPG's to go negative, so where is this motor most happy at in regards to optimum fuel efficiency, i know a loaded question cause there's so many variables.
What I do know at 75 mph or above it goes negative so i want to see where the sweet spot is as close to 75, if its possible. I find it very difficult to keep the speed at 70 it's almost unsafe a lotta speed freaks around here.

 

[SteamiestOyster]

So I think what you are trying to find is the most fuel efficient steady state cruising speed. Steady state meaning you are not accelerating, not changing air intake flow or fuel flow. The best way to figure that out is to find a long, straight, level road and use the instantaneous mpg readout. I would set the cruise control to some speed, drive level at that speed for a few seconds, then press the + button to increment the cruise control speed and keep doing that until you see the mpg peak

 

[9zero1790]

so many factors come into play its tough to really measure as weather and road conditions apply. I have always thought for some reason that whatever the lowest rpm in the highest gear would give me best fuel miles. Im not sure if that is correct but in my mind i am thinking engine working less in 10th gear than 4 etc. I tried doing a longer drive with the cruise at 65 and the mpg did go up a bit but it also felt like slow motion. everyone passed me the entire time. I did notice that at 65 the truck would down shift to 9th and 8th gear for hills easier than when ive done the same roads with the cruise at 70 or 75. so i may not have saved any fuel at all just made myself think i did. every down shift made the instant mpg drop.

 

[dmeyer302]

So I think what you are trying to find is the most fuel efficient steady state cruising speed. Steady state meaning you are not accelerating, not changing air intake flow or fuel flow. The best way to figure that out is to find a long, straight, level road and use the instantaneous mpg readout. I would set the cruise control to some speed, drive level at that speed for a few seconds, then press the + button to increment the cruise control speed and keep doing that until you see the mpg peak

This is the way.

Repeat for 9th and possibly 8th gears. Under 65-70 mph I have noticed my economy is actually better if I leave 10th locked out.

 

[Jason B]

Here is a chart showing gear ratios of the 10R80. Using this, tire size and diff ratio you may be able to calculate RPM for speeds.
10R80 Trans

Ford 10R80 10-Speed Select Shift Automatic Transmissions Gear Ratios
First	4.696:1
Second	2.985:1
Third	2.146:1
Fourth	1.769:1
Fifth	1.520:1
Sixth	1.275:1
Seventh	1.000:1
Eighth	0.854:1
Ninth	0.689:1
Tenth	0.636:1
Reverse	4.866:1

 

[Muffin1]

So I think what you are trying to find is the most fuel efficient steady state cruising speed. Steady state meaning you are not accelerating, not changing air intake flow or fuel flow. The best way to figure that out is to find a long, straight, level road and use the instantaneous mpg readout. I would set the cruise control to some speed, drive level at that speed for a few seconds, then press the + button to increment the cruise control speed and keep doing that until you see the mpg peak

Yes exactly, will try that and I did 90 mile trip today and tried with cruise on going up a grade I shifted onto 9th momentarily it dropped but then up by one & two mpg’s for that incline then back up to 10th where it stabilized, that trip netted me 21.8 I needed to pass a couple times at near 80 so I know that hurts the average.
thanks for the idea.

 

[Muffin1]

This is the way.

Repeat for 9th and possibly 8th gears. Under 65-70 mph I have noticed my economy is actually better if I leave 10th locked out.

Yes I noticed the same in certain situations.

 

[Muffin1]

so many factors come into play its tough to really measure as weather and road conditions apply. I have always thought for some reason that whatever the lowest rpm in the highest gear would give me best fuel miles. Im not sure if that is correct but in my mind i am thinking engine working less in 10th gear than 4 etc. I tried doing a longer drive with the cruise at 65 and the mpg did go up a bit but it also felt like slow motion. everyone passed me the entire time. I did notice that at 65 the truck would down shift to 9th and 8th gear for hills easier than when ive done the same roads with the cruise at 70 or 75. so i may not have saved any fuel at all just made myself think i did. every down shift made the instant mpg drop.

Agreed many variables even fuel quality and actual % of alcohol which is suppose to be up to 10% but who really knows what the blend is.

 

[Muffin1]

Here is a chart showing gear ratios of the 10R80. Using this, tire size and diff ratio you may be able to calculate RPM for speeds.
10R80 Trans

​

Ford 10R80 10-Speed Select Shift Automatic Transmissions Gear Ratios
First	4.696:1
Second	2.985:1
Third	2.146:1
Fourth	1.769:1
Fifth	1.520:1
Sixth	1.275:1
Seventh	1.000:1
Eighth	0.854:1
Ninth	0.689:1
Tenth	0.636:1
Reverse	4.866:1

Thanks for that.

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