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  • Hemi Swap and gear ratios help please

    Hey all, So I'm committed to the hemi swap. I currently have 5.13's for my 08 auto and it was needed for my 35's and 3.8. (measured to 33.5...) and kinda buzzy on the highway. I'm turning 2600 ish at 75mph..

    With the new power levels I will have with the v8 can I use 4.10's instead?

    The 42re and 545rfe have the same final ratio 0.67 so it will be about the same rpms with the hemi. The 4.10's and my tires will be around 2100 rpm at 75 mph..and 1900 at 70mph..

    I do not rock crawl ,it's mostly a mall crawler and grocery getter. I'm pretty pleased with my current setup of 2.5" lift and 35's. I had planned to wait and see what it ran like but I thought I'd ask as I ran across a set of take outs... already beefed up with lockers.


    Thoughts? It's a lot of extra work on top of the swap, I can get these axles for about 4500. And sell mine off for about 2k maybe. I really don't have the extra cash but I can scrounge it up for a good deal. But of i have regear it anyway I'll just run theses...

    Thanks
    bob
    Last edited by norville; 06-06-2017, 12:47 PM.

  • #2
    Originally posted by norville View Post
    Hey all, So I'm committed to the hemi swap. I currently have 5.13's for my 08 auto and it was needed for my 35's and 3.8. (measured to 33.5...) and kinda buzzy on the highway. I'm turning 2600 ish at 75mph..

    With the new power levels I will have with the v8 can I use 4.10's instead?

    The 42re and 545rfe have the same final ratio 0.67 so it will be about the same rpms with the hemi. The 4.10's and my tires will be around 2100 rpm at 75 mph..and 1900 at 70mph..

    I do not rock crawl ,it's mostly a mall crawler and grocery getter. I'm pretty pleased with my current setup of 2.5" lift and 35's. I had planned to wait and see what it ran like but I thought I'd ask as I ran across a set of take outs... already beefed up with lockers.



    Thoughts? It's a lot of extra work on top of the swap, I can get these axles for about 4500. And sell mine off for about 2k maybe. I really don't have the extra cash but I can scrounge it up for a good deal. But of i have reheat it anyway I'll just run theses...

    Thanks
    bob
    I run 4.10 gears here in the altitude with good power. I can pull the 7 mile climb up the West side of the Eisenhower Tunnel @ 80 - 85 MPH in high gear. I do have the newer Transmission though. My OD is .80. You will be fine running these Mountains in 3rd gear. On flatter terrain you will cruise easily in OD. You will love the V8!! My Engine turns 2400 RPM @ 70 MPH with 35" Duratracs.
    2012 JK 2 Door 2.5" AEV lift/ Fuel Hostage17 x 9 wheels, with Nitto 295x70 x 17 Tires. Warn Vr8000, Elite Bumper, LOD rear bumper, Teraflex tire carrier. Wife's Jeep!

    My Jeep. 2014 JKU, 6.4L Hemi AEV kit, 2.5" AEV lift, 35" Duratrac's. Gen Right aluminum bumpers, Warn VR 8000 winch. Pro Rock 44.

    Comment


    • #3
      Originally posted by scubatech View Post
      I run 4.10 gears here in the altitude with good power. I can pull the 7 mile climb up the West side of the Eisenhower Tunnel @ 80 - 85 MPH in high gear. I do have the newer Transmission though. My OD is .80. You will be fine running these Mountains in 3rd gear. On flatter terrain you will cruise easily in OD. You will love the V8!! My Engine turns 2400 RPM @ 70 MPH with 35" Duratracs.

      Great info as I plugged in your numbers 4.10 with the .83 OD (wa580) and it's almost the same as my 5.13s and .67 od (545rfe 03-05)..

      I don;t quite have the hills you do

      http://www.grimmjeeper.com/gears.html

      Comment


      • #4
        2600rpm at 75mph doesn't seem bad to me. Not sure if regearing will be worth the cost.

        My '14 with the 3.6L, 4.10s and the same size tires runs about that same rpm, if not higher, at 75 mph. I actually want to regear to 4.56 to help get up these mountain grades.
        2014 Granite JKUR w/expo stuff

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        • #5
          I have 4.88s with my 5.7 Hemi and 37s (Bfg Ko2) and sometimes wish I just stuck with 4.10s


          Sent from my iPhone using Tapatalk

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          • #6
            Originally posted by redrockjk View Post
            I have 4.88s with my 5.7 Hemi and 37s (Bfg Ko2) and sometimes wish I just stuck with 4.10s


            Sent from my iPhone using Tapatalk

            To much rpm at highway speeds or ?

            Comment


            • #7
              Originally posted by norville View Post
              To much rpm at highway speeds or ?


              Yes, Hemis like to be in the 2000-2100 rpm sweet spot. Plus if you have a rubicon you have low enough gearing for anything Offroad


              Sent from my iPhone using Tapatalk

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              • #8
                I have a sahara , and I swapped out the stock 3.73s for these 5.13s and with the auto it has more pickup and better road manors than when it was on stock tires... It's not popping in and out of OD .. It's still a slug in the midrange I just don;t want to sink any money into this 3.8 and 42r that's why I'm going 5.7...

                I guess it's best if I try these out and see how it works for me. I'll just keep an eye out if another good deal pops up.

                bob

                Comment


                • #9
                  Originally posted by norville View Post
                  I have a sahara , and I swapped out the stock 3.73s for these 5.13s and with the auto it has more pickup and better road manors than when it was on stock tires... It's not popping in and out of OD .. It's still a slug in the midrange I just don;t want to sink any money into this 3.8 and 42r that's why I'm going 5.7...

                  I guess it's best if I try these out and see how it works for me. I'll just keep an eye out if another good deal pops up.

                  bob
                  Good thinking!! The 6.4 Liter is a revving machine kinda like the 3.6L. When you nail it the thing will go to 6500RPM pretty quickly. I haven't driven a 5.7L to compare to.
                  2012 JK 2 Door 2.5" AEV lift/ Fuel Hostage17 x 9 wheels, with Nitto 295x70 x 17 Tires. Warn Vr8000, Elite Bumper, LOD rear bumper, Teraflex tire carrier. Wife's Jeep!

                  My Jeep. 2014 JKU, 6.4L Hemi AEV kit, 2.5" AEV lift, 35" Duratrac's. Gen Right aluminum bumpers, Warn VR 8000 winch. Pro Rock 44.

                  Comment


                  • #10
                    Originally posted by norville View Post
                    I have a sahara , and I swapped out the stock 3.73s for these 5.13s and with the auto it has more pickup and better road manors than when it was on stock tires... It's not popping in and out of OD .. It's still a slug in the midrange I just don;t want to sink any money into this 3.8 and 42r that's why I'm going 5.7...

                    I guess it's best if I try these out and see how it works for me. I'll just keep an eye out if another good deal pops up.

                    bob
                    Good thinking!! The 6.4 Liter is a revving machine kinda like the 3.6L. When you nail it the thing will go to 6500RPM pretty quickly. I haven't driven a 5.7L to compare to.
                    2012 JK 2 Door 2.5" AEV lift/ Fuel Hostage17 x 9 wheels, with Nitto 295x70 x 17 Tires. Warn Vr8000, Elite Bumper, LOD rear bumper, Teraflex tire carrier. Wife's Jeep!

                    My Jeep. 2014 JKU, 6.4L Hemi AEV kit, 2.5" AEV lift, 35" Duratrac's. Gen Right aluminum bumpers, Warn VR 8000 winch. Pro Rock 44.

                    Comment

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