Gear question 3.73 or 4.11?? that is the question

Discussion in 'General IH Tech' started by waterhound, Oct 12, 2017.


  1. waterhound

    waterhound Farmall Cub

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    The Scout 2 has a 345 - 727 auto - dana 20... with 33" tires . Im looking for a solid daily driver with decent trail capabilities and around town driving
    Back story..
    I am rebuilding a 71 scout 2.. it currently is stripped down to the tub, frame and axles

    Currently the axles are front dana 30 and rear dana 44 with 3.73 gears
    I acquired a detrtoit truetrac limited slip for the rear and the master install kit already
    I have an extra front dana 44 w 3.54 that I am swapping in and need to do a gear swap - big question is do I install 3.73 in the front Dana 44 and the locker with stock gears in the back OR
    all new 4.11 in front and back with rear posi locker in the rear
    The gear ratio chart I read shows both are good just curios what yall think

    Either way, I have to buy one gear set and two install kits for front re-gearing and switching carriers in the rear..

    Money wise I really only have to buy one more gear set to switch to 4.11 unless I go used

    IF I could go used -- As I have access to a good used 3.73 front gearset AND a really clean good front and rear set of 4.11 thick gear and pinions which is needed for my 3.73 and down carriers

    I have called Xdiff, Randys, and 4wheel to talk about options and part numbers BUT it all boils down to
    3.73 gears OR 4.11 gears which is best ---- for my application ----- watchta think???
     
  2. BigRigg

    BigRigg High Wheeler

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    You say daily driver. Freeway? Stop and go traffic? Small town? Metro?

    I LOVED 410s and 33s. And my scout was a daily driver, but it was back roads, 55 mph tops. If I were traveling on a freeway, and trying to keep up with modern traffic, 373 would be better.
     
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  3. Darrel

    Darrel High Wheeler

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    What BiggRigg said. I had 4.10s and 33s at one time as well and they weren't great at modern speeds. At 65 you're looking at 2800-2900 RPMS. I would go 3.73s myself.
     
  4. Sammy

    Sammy High Wheeler

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    I once had the same setup 3.73 and 33's and was good on the highway, but 90% of my commute was highway so was perfect for me. Really comes down to where you're going to drive but I would stick with the 3.73.
     
  5. stroker3

    stroker3 High Wheeler

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    What they said.
    4.10's if you never plan on driving at today's normal speeds.
     
  6. BinderBookie

    BinderBookie High Wheeler

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    With a torquey 345, you have a lot more leeway than if you had a less potent engine.

    Considering it will mostly be pavement driving, the 3.73:1/33 inch tire scenario will work fine and is roughly equivalent to the stock tire size and 3.54:1 ratios (equivalent to about a 3.25:1 ratio). Acceleration performance will not be as snappy as 3.73 and stock 29 inch tires was but it will drop 200+ rpm at 60 mph.

    Going to 4.10s and 33s will put you in the same ballpark as the current 3.73 with 29 inch tires. According to the equivalent ratio formula, you'd need 4.27:1 to match the old combination exactly, but 4.10s are close.

    Think hard on how you intend to use the Scout. If it's just an occasional driver, I think you will be happier performance-wise with 4.10:1... both on the street and four wheeling. The hit in fuel economy won't bother you much if it's driven just a few thousand miles per year. If you put 10,000 plus a year on it and it's a mainstay transport rig that's drive on the highway a lot, the lower gears might be the best choice and save some gas. One thing to bear in mind is that a lower geared rig driven mostly in the city gets somewhat better mpg in stop and go traffic than a taller geared one. If its driven on the highway, then the drop in rpm from taller gears can pay off better mpg-wise. Trail performance is always better with lower ratios.
     
  7. MrKenmore

    MrKenmore High Wheeler

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    I think Jim offers some excellent advice. 4.10's will probably make you happier overall. But once you jump on the highway and you're howling at 3,000 RPM doing 70 MPH you might get annoyed. Not that it's bad, just a lot of RPMs.
     
  8. waterhound

    waterhound Farmall Cub

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    I live in Austin TX with plenty of highway driving and some 80mph toll roads. I take mostly back roads to work but would like to able to drive on highways. I don't necessarily need to be with traffic but don't want to run over.

    At some point I will doing a LS swap (as I already have the 5.3 long block and Jeep dana 300 with 700r4 and 4l60e adapters.) but probably not for at least a year or two

    Lets talk about ratios for a minute I used www.Grimmjeeper.com website to do a complete comparison for stock 33 tires w 3.73 against 33 with 4.10
    He has a slick website I entered 727, and dana 20 for both sides and one side 33" with 3.73 and 33" with 4.11
    see below

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


    33 with 3.73
    Road speed at given RPM in miles per hour
    Gear
    750 RPM 3000 RPM 6000 RPM
    1 8 31 61
    2 13 52 103
    3 19 75 150

    Road RPMs at given speed in miles per hour
    Gear 10 35 70

    1 983 3441 6882
    2 582 2036 4073
    3 401 1404 2809

    33 with 4.11

    Road speed at given RPM in miles per hour
    Gear
    750 RPM 3000 RPM 6000 RPM
    1 7 28 55
    2 12 47 94
    3 17 68 136
    Road RPMs at given speed in miles per hour
    Gear 10 35 70

    1 1083 3791 7583
    2 641 2244 4488
    3 442 1547 3095

    What I notice here is only a 200 rpm difference at 70
     
  9. Sammy

    Sammy High Wheeler

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    If you take into account the 286 rpm difference at 70 with the 4.11, at the same rpm 3095 you would be doing 77 with the 3.73
     
  10. MrKenmore

    MrKenmore High Wheeler

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    If an OD transmission is in your future as well as an LS conversion I suppose the 4.10 would be the winner.
     
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  11. waterhound

    waterhound Farmall Cub

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    hmm tough call....
     
  12. Darrel

    Darrel High Wheeler

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    That additional info actually makes the choice a lot easier. With a 7004r in your near future I would absolutely go with the 4.10s as it has a generous overdrive of 0.70. 4.10s/700r4 OD will put your RPMs at 65mph around 2000 RPMS which is sweet. Even at 85mph you'll only be turning about 2500 RPMs. Believe me you will be super happy with that combo.

    The 3.73s/700r4 OTOH will be more like 1800 RPMs at 65mph which will cause a small block to lug (or downshift) way too much on hills. The 3.73s will maybe get better mileage, but the cost savings would really only come into play if you put a lot of miles on it over a number of years.

    One tip. When doing your calculations look up the specs for your tires or better yet measure them. Usually 33s will in actuality only measure 32.5 or even 32 inches which will increase your RPMS noticeably. Also a non-lock up 727 will turn more RPMs at speed than a lock-up trans like the 700r4. I haven't measured it on a 700r4 with a factory converter, but a 150-200 RPM drop under lockup is probably typical. Some online calculators will automatically add RPMs (torque converter slip) for a non-OD trans, but not all.

    727 or 700r4 I would not worry about offroading as the 4.10s won't make that much difference at all over the 3.73s. And that's coming from a pretty serious offroader. Plus, if you find yourself wanting for power all you have to do is drop it to low range. Regardless that steep first gear in the 700r4 will pull either 3.73s or 4.10s off the line plenty well.
     
  13. BigRigg

    BigRigg High Wheeler

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    I agree with Darrel. Now that we know a swap is in the future, 4.09 no question. If you've ever considered 35" tires, then I'd even recommend 4.27 gears.
     
  14. TheScoutMaster

    TheScoutMaster High Wheeler

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  15. waterhound

    waterhound Farmall Cub

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    Thanks for all the great info.
     
  16. Erik VanRenselaar

    Erik VanRenselaar Y-Block King

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    I like my 3.73 axles with the 33" tires. Great on the freeway and around town, even with the 304 engine. I made up for any loss in the low speed end by swapping a Dana 300 transfer case in place of the stock Dana 20. Low range moved from 2.03:1 to 2.61:1. I also installed a low 1st/2nd planetary gearset in my 727 auto trans. It really makes a difference at the slower speeds and uphill crawls.
     
  17. scoutpappa

    scoutpappa Farmall Cub

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    33" KM2's and 3.73 with the 727 as well. In Houston, so in some cases I would like a 3.54 but the 3.73's are the best compromise I can think of based on really mixed driving. I could go 35's to cheat the gearing even higher but I love the look of 10.50's and unless I want to go Interco then the choices are slim sticking with stock wagon wheel 15's. Of course I could go overland with 16's and buy some odd ball 34 ish x 10 ish tire but that puts me in the same situation.
     

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