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Thread: Regear with 38s

  1. #21
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    Quote Originally Posted by SSinGA View Post
    My sons Jeep is a 14 JK 3.6l auto trans with 5.13 gears and BFG 37” tires. It’s way too much IMO. Maybe good for more mountainous terrain but here at 70mph it’s turning almost 3k RPM. Swapping them out for 4.56 gears in the next few weeks.
    Serously, what is the difference between running 2700 at 70 or 3000 at 70? Please dont tell me fuel mileage.... because fuel mileage is going to be more based off engine load than RPM. You will most likely get worse fuel mileage with 4.56's at 70 than 5.13s..... IMHO, from experience, your making a mistake changing gears.

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    Quote Originally Posted by DirtyLuLu View Post
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  3. #23
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    Quote Originally Posted by Brian View Post
    Serously, what is the difference between running 2700 at 70 or 3000 at 70? Please dont tell me fuel mileage.... because fuel mileage is going to be more based off engine load than RPM. You will most likely get worse fuel mileage with 4.56's at 70 than 5.13s..... IMHO, from experience, your making a mistake changing gears.
    I guess weíll see soon.

  4. #24
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    Regear with 38s

    Quote Originally Posted by Brian View Post
    Serously, what is the difference between running 2700 at 70 or 3000 at 70? Please dont tell me fuel mileage.... because fuel mileage is going to be more based off engine load than RPM. You will most likely get worse fuel mileage with 4.56's at 70 than 5.13s..... IMHO, from experience, your making a mistake changing gears.
    I think you will see a small increase in the mpg.




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    Last edited by Pthorpe84; 03-24-2018 at 07:50 AM.
    2015 JKU Hard Rock, 3.5" Game Changer-Rock Sport, 37" Toyo M/T, Overline Fenders, M/C Full Stinger Bumper, GenRight Fusion Rear Stubby Bumper, Poison Spyder Tire Carrier, M/C Rock Sliders, Warn Power Plant HD, Viair Constant Duty with Tank, 17" ATX Slabs, Evo Skid Plates, Cheap Chinese Lights, Factor 55 Flat Link, ApolloIntec Switch Pod, 48" Hi-Lift, Dynomax Exhaust

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  5. #25
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    Quote Originally Posted by Pthorpe84 View Post
    I think you will see a small increase in the mpg but not much. But where it will help is that you can use O/D more instead of always using 5th gear. Plus the ability to climb a hill at highway speeds Vs losing speed and down shifting.


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    He is going from 5.13 to 4.56. Should be the exact opposite of what you said. Come on Bear Poker.

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  6. #26
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    Yeah I I just edited the post. Iím a dumb ass bear poker. But if itís highway use mainly he should be good to go. Maybe itís really flat where he is vs hills


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  7. #27
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    Quote Originally Posted by Brian View Post
    Serously, what is the difference between running 2700 at 70 or 3000 at 70? Please dont tell me fuel mileage.... because fuel mileage is going to be more based off engine load than RPM. You will most likely get worse fuel mileage with 4.56's at 70 than 5.13s..... IMHO, from experience, your making a mistake changing gears.
    Engine heat? And maybe not as much in OD, but when downshifting for hills?

  8. #28
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    Quote Originally Posted by chitown35 View Post
    Engine heat? And maybe not as much in OD, but when downshifting for hills?
    Engine heat, in this case is also based on load. When downshifting down hill, higher rpm would be best. No matter how you slice it, changing from 5.13 to 4.56 is not a smart more over 250 rpms.

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  9. #29
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    Quote Originally Posted by Brian View Post
    Engine heat, in this case is also based on load. When downshifting down hill, higher rpm would be best. No matter how you slice it, changing from 5.13 to 4.56 is not a smart more over 250 rpms.

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    Unless your high RPMs are putting you into an inefficient band in the engine, right? Which, again, not at 3000 RPMs, but how many RPMs are you at in lower gears going UP a steep pass at 75mph? In my experience this is where temps spike.

  10. #30
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    Quote Originally Posted by chitown35 View Post
    Unless your high RPMs are putting you into an inefficient band in the engine, right? Which, again, not at 3000 RPMs, but how many RPMs are you at in lower gears going UP a steep pass at 75mph? In my experience this is where temps spike.
    Your temps would be spiking because of the load on the engine not because of the RPM

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