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2021 3.5 eb 3.31 vs 3.55 mpg

Frank_N

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Is there a difference in mpg for a 2021 3.5 eb with 3.31 or 3.55 axle with stock 33" tires?
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AutonomousHybridF150

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The truck gets the same MPG because Ford addresses the rear end gear via changing ratio for 10th gear on those transmissions.

At least this was what I concluded many years ago when I tested it.
 

hardlymoving

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Is there a difference in mpg for a 2021 3.5 eb with 3.31 or 3.55 axle with stock 33" tires?
The gear ratio for 10th gear for the Ford 10R80 ten speed transmission is .63 to 1.0 in all versions. I can only say that I am satisfied with the gas mileage of my 2021 3.5 Ecoboost, 4 x 4 with the 3.55 axle ratio. Have averaged 19.3 mpg on the DIC indicator on the dash ( and the DIC indicator is only slightly optimistic compared to hand calculations) which is good considering that I drive on a lot of dirt/gravel roads. Conventional wisdow would dictate better gas mileage with the 3.31 axle ratio but I'm not so sure that is true in actual practice as the transmission may be shifting down to lower gears more often with the 3.31. It would be interesting to hear from others having the 3.31 axle ratio.
 

RJL1400

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The gear ratio for 10th gear for the Ford 10R80 ten speed transmission is .63 to 1.0 in all versions. I can only say that I am satisfied with the gas mileage of my 2021 3.5 Ecoboost, 4 x 4 with the 3.55 axle ratio. Have averaged 19.3 mpg on the DIC indicator on the dash ( and the DIC indicator is only slightly optimistic compared to hand calculations) which is good considering that I drive on a lot of dirt/gravel roads. Conventional wisdow would dictate better gas mileage with the 3.31 axle ratio but I'm not so sure that is true in actual practice as the transmission may be shifting down to lower gears more often with the 3.31. It would be interesting to hear from others having the 3.31 axle ratio.
I ordered the 3.31 because I really didn't know what difference it would make. What does the different ratios actually do?
 
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Frank_N

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I ordered the 3.31 because I really didn't know what difference it would make. What does the different ratios actually do?
A higher gear ratio increases your RPM's slightly. Typically higher RPM's would affect fuel economy but I am not sure about that with the 3.5 eb. I have read that at highway speeds and lower RPM's, the turbo may be coming on and decreasing overall fuel economy.
 

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RJL1400

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A higher gear ratio increases your RPM's slightly. Typically higher RPM's would affect fuel economy but I am not sure about that with the 3.5 eb. I have read that at highway speeds and lower RPM's, the turbo may be coming on and decreasing overall fuel economy.
Got it!
 

ATLalien

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All things being equal; the higher gear ratios will have a little better initial acceleration, but may have a lower top end with higher RPMs. Fuel economy would also be a little worse for higher ratios. The difference may be a little or a lot depending on the ratios you're comparing and a bunch of other factors.
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