3.31 to ???

3.31 to ???

This is a discussion on 3.31 to ??? within the F150 Ecoboost Towing forums, part of the F150 Ecoboost Forum category; Hello! My wife and I just set off on an adventure for the rest of the year to the end of the road in Alaska, ...

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Thread: 3.31 to ???

  1. #1
    Ecoboost Sr Member avwizz's Avatar

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    3.31 to ???

    Hello! My wife and I just set off on an adventure for the rest of the year to the end of the road in Alaska, Prudhoe Bay. Weíre in Georgia now and Iím considering the possibilities of a gear change. Tires are stock size for those wondering.

    I was estimating 9mpg but am getting 8.5-9 and thatís just in the south east.
    Obviously if we were to change the difference in MPG would almost never make up the cost of the change but weíre looking at close to 20k miles with this set up.

    I know some of the responses will be ďsell your truck, itís not worth the changeĒ or dump some of your stuff/change tiresĒ but this is what weíre rolling with.

    So math wise at 70mph (weíre usually a little slower but thatís easy math)

    3.31 @ 2000
    3.73 @ 2250
    4.10 @ 2450

    What would go with? Any experience towing at those gears? Especially the 4.10.




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  2. #2
    Ecoboost Regular J-Winship's Avatar

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    3.73 would be a normal towing gear for that truck. But why the change? You never said that.


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    Eco-Beast noodles's Avatar

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    I usually lock out 6th gear when I tow (3.31). I like my towing rpms between 2500-3K rpm.
    13 SuperCrew Ruby Red 302A, 4x4 6.5 box, 3.31, Roush 22's. Twin catch cans, "leveled" with Bilsteins (-2 front, -3 rear), AirLift, SCT. Other's may have displacement on demand... I have an endless supply of torque at my right foot's demand.


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    Ecoboost Regular J-Winship's Avatar

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    I would stick with the gear set you have and keep locking out 6th. Or go with 4:10 setup. I have a 3:31 setup I do the same with. Also a 3:73 I still lock out 6th. Also have a 3:55 setup with the 10speed and 9and 10 get locked out. 4:10s might be what youíre looking for. But youíll always be that way even empty. If itís not a FULL TIME towing truck just lock out 6th and call it a day. Less stress on the trans anyway being in less of an overdriven pulling a load.


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    Ecoboost Pro Mulyhuntr's Avatar

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    70 mph was around 2k rpms in my 2014 with 275/65-18ís and stock 3.73ís. Your tireís must be much smaller? Is the gear change for mileage or towing power? Donít waste your money if youíre trying to improve mileage.

  7. #6
    Ecoboost Sr Member avwizz's Avatar

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    Quote Originally Posted by J-Winship View Post
    3.73 would be a normal towing gear for that truck. But why the change? You never said that.


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    True it wasnít directly stated. Reasons would be potentially better MPG. Better performance, better for the truck long term over the course of the trip.


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  8. #7
    Ecoboost Sr Member avwizz's Avatar

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    Quote Originally Posted by noodles View Post
    I usually lock out 6th gear when I tow (3.31). I like my towing rpms between 2500-3K rpm.
    I always lock out 6 but even in 5th itís just at 2k rpm. Been messing with 4th and at 65 itís at 2500.


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    Ecoboost Veteran mj0528's Avatar

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    Quote Originally Posted by J-Winship View Post
    I would stick with the gear set you have and keep locking out 6th. Or go with 4:10 setup. I have a 3:31 setup I do the same with. Also a 3:73 I still lock out 6th. Also have a 3:55 setup with the 10speed and 9and 10 get locked out. 4:10s might be what youíre looking for. But youíll always be that way even empty. If itís not a FULL TIME towing truck just lock out 6th and call it a day. Less stress on the trans anyway being in less of an overdriven pulling a load.


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    What are your rpms in 8th when running 60 or 65?

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  10. #9
    Ecoboost Regular J-Winship's Avatar

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    Quote Originally Posted by mj0528 View Post
    What are your rpms in 8th when running 60 or 65?

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    In 8th at 60 Iím about 1900 rpm. 7th puts it about 2250.


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  11. #10
    Eco-Beast mass-hole's Avatar

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    Your RPM's don't sound quite right. 32" tire is about stock.

    Here is my calculator on google drive for both the 6 speed and 10 speed trucks. You can punch in a speed, tire OD, and pick which transmission gear you want it to display the RPM's of on the left in the green cells.

    https://drive.google.com/open?id=1Eu...-CXOGL-b2rAy9c

    I don't really think you need more than 3.73's on stock tire size. I live in the mountains in Utah and my truck has 3.73's and does great.

    I also wouldn't expect much of an improvement in MPG. I get 10 at best.
    Last edited by mass-hole; 03-05-2019 at 12:55 PM.
    Mitchf150 likes this.
    2014 Lariat Screw, 157", Max Tow, 502A - Gearhead Tuned, AFE CAC, CRP Manifolds, RX Catch Can, Bilstein 5100, AirLift RideControl, 275/60R20 Wrangler Duratracs

    2006 Jeep Liberty CRD(diesel) - GDE Tune, Straight piped, AFE filter, GTB2060 custom build turbo, 2.5" Lift, ARB bumper, 4.10's, Detroit Truetracs F/R

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