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What RPM is the V6 most happy with at cruise speed

Discussion in 'Early CJ5 and CJ6 Tech' started by DanStew, Jul 3, 2005.

  1. Jul 3, 2005
    DanStew

    DanStew Preowned Merkin salesman Staff Member

    Lexington, South...
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    Trying to figure out gear ratios and what not and what i should run in the bus. I am thinking it maybe cheaper for me to get 5.38 gears since there are plenty of dana 44s around with them in them, but at 65 the jeep would be running 2571 RPMs aat 65 MPH. given i wont be running 65 much i drive the jeep to work and such, but nothing on highway since it is so vicious down here. I am wondering what the V6 is happy with at RPM land. I know with the 3.54 gears in the waggie axles now i can defiantely cruise alot faster, but just wanting to get back a little more low range for the trails. This isnt really a quesion about what gears to get, jsut need to know the happy RPMs for the V6 :)

    thanks!
     
    DanStew, Jul 3, 2005
    #1
  2. Jul 3, 2005
    61CJ5

    61CJ5 Member

    Lafayette, CA
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    Do you have an overdrive, or did i screw up my math. I'd be very happy with 2500 at 65mph. With my 4.88's and 35 inch tires i think im looking at like 3200 RPM at 65, going off of memory.

    At any rate, im interested in the answer to your question.
     
    61CJ5, Jul 3, 2005
    #2
  3. Jul 3, 2005
    DanStew

    DanStew Preowned Merkin salesman Staff Member

    Lexington, South...
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    Nope no overdrive, lost that option once i installed the dana 20 :(
     
    DanStew, Jul 3, 2005
    #3
  4. Jul 4, 2005
    william_cj3b

    william_cj3b 3BOB driver

    Milton, FL
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    Nov 17, 2003
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    Dan, I run 70-75 pretty regulary and have done so for long distances in the past. With 3.73's and 235/75 radial that puts me at about 3300 rpm. She's really talkin' at that speed (burnt out glasspacks) but it doesn't seem to hurt anything. There is kind of a sweet spot with mine where it isn't lugging and isn't wound up like a top between 45 and 55 MPH (between 2000 and 2500 rpm) I have plenty of power to climb hills or pass with out downshifting and those speeds.

    O/T - 3.54's :shock: You're running 34" LTB's right? How's the drivability? Off the line? I'm wanting to go the same setup as Budd (Jeepster BBS) had until recently. I'd like to compromise between rpm and driveability when I regear. If yours is drivable I might just see what it will do with the 3.73's.
     
    william_cj3b, Jul 4, 2005
    #4
  5. Jul 4, 2005
    Chris Insull

    Chris Insull All roads lead me back to the beach... 2023 Sponsor 2022 Sponsor

    Chesapeake, VA.
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    The peak torque for the 225 is at 2400 RPM (per FSM). With my OD, I usually cruise at 2800 RPM on the hiway and still have plenty of motor left for passing, etc... I'm not real fond of driving with RPM over 3000 for any length of time. Around town, I don't even use the OD and it seems happy to putt around at about 1000 RPM (or below).
     
    Chris Insull, Jul 4, 2005
    #5
  6. Jul 4, 2005
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    Dan, I think you better check your math. I get 3357 RPM @ 65 mph with 35" tires.

    Still, your engine would be fine at that speed. Maybe not the quietest or best economy, but well within the normal operating range.
     
    timgr, Jul 4, 2005
    #6
  7. Jul 4, 2005
    DanStew

    DanStew Preowned Merkin salesman Staff Member

    Lexington, South...
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    It is driveable right now, not like i have been driving it much but i do notice i cruise better on the roads.Given the jeep is more trail vehicle, i only reeally take it to work,

    Here is the calculator i am using, pretty cool since i can do 2 calculations side by side

    http://www.dfw-tx4wd.org/Tech-Dept/Tech-Dept/gears.html


    Still devating on going to lower Tcase gears but the Dana 20, i think it really is not that low of a gear to justify it
     
    DanStew, Jul 4, 2005
    #7
  8. Jul 4, 2005
    DanStew

    DanStew Preowned Merkin salesman Staff Member

    Lexington, South...
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    HHHMMMM.. going throguh the calculator. I didnt realize going throguh final crawl ratio, if i just did the 3.15 low gear for the dana 20 it gets me to 82.96 crawl ratio with the 3.54 axle gears. If i kept the dana 20 stock with 2.02 ratio and went with 5.38 gears, the crawl ratio is 81.26. I am guessing the i am wrong with the low gear kit not doing anything. Since i am going mearly by "numbers" bumping the 2.02 to 3.15 in the dana 20, I thoguht it was not as drastic as going from 3.54 to 5.38 in axle gears. But i am wrong. I could go all sick and do both but i really do not need to go rock star crawler low gear. I just wanted to go back to what i was used to with the dana 18 and 4.27 gears.. and a little lwoer with the T18 tranny i instllaed.

    Is the reason for the differnce with the ratios is that the Tcase is closer to the torque source and multiplies it differntly??
     
    DanStew, Jul 4, 2005
    #8
  9. Jul 4, 2005
    Willy-N

    Willy-N Member

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    Mine likes 2,800 to 3,100 RPMs just fine. Seems to purrrr nice around that range on the flat open road. I like the 5.38 gears for going slow it still keeps the RPMs up so to not over heat or lug the engine when crawing for long distance off road on rough surfaces. I am running 31 inch tires on mine and very happy with the gear ratios. The Overdrive is nice on the open road and to match gears off road for that perfect RPM. Mark
     
    Willy-N, Jul 4, 2005
    #9
  10. Jul 4, 2005
    fourtrail

    fourtrail Built not Bought

    Carlinville,...
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    3.54x3.15=10.8676
    5.38x2.02=11.151

    When in low range there is not much of a difference. The big change is when in high range.
     
    fourtrail, Jul 4, 2005
    #10
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