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Gear Ratio Suggestion!

Discussion in 'Flat Fender Tech' started by Vhunter, Jan 10, 2006.

  1. Jan 10, 2006
    Vhunter

    Vhunter Member

    Redding, California
    Joined:
    Jun 26, 2005
    Messages:
    262
    Hello Guys, I have under-construction a Cj3B with a 225 V6 and need advice on a gear ratio. I have been to the websites on how to calculate RPM by rear-end ratio, but what is an ideal RPM range at 65 mph for a V6? My question is at what RPM should this engine be at for best performance while cruising down the HWY. I'm going to run a ford T18 four speed and put a low ratio gear set in the Dana 20 TC so I don't have to have an overdrive. Besides the Dana 20 with its straight through power in 2 wheel drive sure lowers the noise level.
     
    Vhunter, Jan 10, 2006
    #1
  2. Jan 10, 2006
    lynn

    lynn Time machine / Early CJ5 HR Rep Staff Member

    Huntingdon PA
    Joined:
    Sep 20, 2002
    Messages:
    3,437
    What size tire are you planning to run?

    I run a V6, with a T18, 3.73 gears and 33" tires.
    I turn about 2200 rpm at 60/65 mph on the highway. I'd think ideal rpm would be around 2500/2700. On the street, the combo I run is a bit slow off the line. It was better when I ran 31" tires, but I can live with the 3.73s and 33s as is.

    So I'd say for 31" tires, 3.73 is good. You'll have the T18 and low gear set in the D20 to get your crawl ratio down offroad.
    If you plan to run 33s, then I'd say 4.10 or 4.27 are good ratios for street and trail, with 3.73s as the tallest acceptable ratio for 33s.
     
    lynn, Jan 10, 2006
    #2
  3. Jan 10, 2006
    Vhunter

    Vhunter Member

    Redding, California
    Joined:
    Jun 26, 2005
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    262
    I plan on running 33's, but I may run 35's later on if I find I need more clearance. I am not going to go to spring over for clearance and want to stay with spring under for better control. So, do you think that 2500/2700 rpm range is where this motor should be at doing 65?
     
    Vhunter, Jan 10, 2006
    #3
  4. Jan 10, 2006
    lynn

    lynn Time machine / Early CJ5 HR Rep Staff Member

    Huntingdon PA
    Joined:
    Sep 20, 2002
    Messages:
    3,437
    That's my guess... the engine would be more responsive at 2500/2700... I'm not sure of the ideal rpm for maximum efficiency... I think the 2200 I run is a tad low. Hopefully others will chime in here with more input...
     
    lynn, Jan 10, 2006
    #4
  5. Jan 10, 2006
    jeepdaddy2000

    jeepdaddy2000 Active Member

    Eagle Point oregon
    Joined:
    Jun 24, 2004
    Messages:
    1,165
    The V6 is a great low RPM motor with lots of torque. I would like to stay in the low 2's for crusing. This is much easier for you, since you are planning to install the T18A. You might want to put off installing the T case gears till you run the trans. The compound low will suprise you. Again, tire size will determine gear ratio.
     
    jeepdaddy2000, Jan 10, 2006
    #5
  6. Jan 14, 2006
    willysworker

    willysworker Member

    Joined:
    Oct 12, 2003
    Messages:
    172
    what he said. plus my thought, CJ7's were invented for higher speeds.
     
    willysworker, Jan 14, 2006
    #6
  7. Jan 15, 2006
    Kodiak12060

    Kodiak12060 Sponsor

    Beacon NY
    Joined:
    Sep 27, 2002
    Messages:
    465
    Anyone have a location for the HP and Torque curve of the stock 225 V6 as used in the jeep. What about the redline?
     
    Kodiak12060, Jan 15, 2006
    #7
  8. Jan 15, 2006
    Southtowns27

    Southtowns27 Custom Title

    The Backhills of...
    Joined:
    Feb 4, 2003
    Messages:
    536
    I had 3.73's and 31" tires behind my 225. I think the factory built it like that for a reason. It wasn't a rocket, but seemed to work well enough. It was geared a little high off-road, but I only had a 3 speed, not a "granny" 4 speed. The 3.73's will give you good mileage too. I have the set here that I removed from my Jeep if you're interested. The fit a Dana 44 and a Dana 27 front. I went and put in a V8 with 4.89's and an OD :rofl:
     
    Southtowns27, Jan 15, 2006
    #8
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