Gear Ratio upgrade for 69 GTX

General Mopar Tech Discussions

  1. Steve69GTX

    Steve69GTX New Member

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    I just got a 69 GTX it's 440 4 barrel with a 727 auto trans. The car has 3.23:1 rear end gear ratio. I bought it knowing it had a rear end noise. The repairs require basically redoing most the rear end. My question is should I keep it the stock 3.23 or increase it?

    The shop where the rear end is being done suggested leaving it be. He said there is not enough noticeable difference from the 3.23 to a 3.55 for the money and going to a 3.73 or bigger would make the car unbearable on the highway.

    I don't plan on doing a ton of highway driving and do not necessarily want a car with no guts when I mash the pedal. At the same time, I don't want my muscle car to be restricted to Highway speeds of 55-60 mph.
     
  2. evanbrendel

    evanbrendel Well-Known Member

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    well 323 sounds like a good gear if you want to run the speed limit on the highway i had 355 and could but it was running 3200 or so at 70
     
  3. Meep-Meep

    Meep-Meep дворянин

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    With a 440 and an auto 3.23 is a good choice. If you want better 1/4 mile performance, then 3.55 or 4.10 for sure, but as already mentioned freeway driving won't be as nice.
     
  4. 69 Runner

    69 Runner ADMIN wif a corner office (Deceased - RIP)

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    Here's a pic I took while on a lil highway cruise in my Duster. 360, auto, 3.91's. Runs just fine.

    You also need to consider the stall speed on your converter. If it's to high and you're geared to high (low numerically) then you might generate a lot of heat in the trans and burn it up

    P0002374.jpg
     
  5. 5wndwcpe

    5wndwcpe Huge Member FBBO Gold Member

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    I'd run the 3.55's as well. Oh, and welcome to the board.
     
    Last edited: Apr 10, 2009
  6. daredevil

    daredevil Well-Known Member

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    i was gonna say 391 with some tall tires
     
  7. 5.7 hemi

    5.7 hemi FBBO Gold Member FBBO Gold Member

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    Yeah, 3.91 and tall tires should do the trick.
     
  8. Gary67

    Gary67 Well-Known Member

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    Go to Randy's ring and pinion and use the calculator. Sounds like you have an idea what you'd be comfortable with. He used to have a 3:73 ratio, but I'm not sure what case it was for...FWIW I have 3:55's in my GTX. nice difference from the 3:23's it had.
     
  9. Rob R

    Rob R Well-Known Member

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    A old rule of thumb was that for every step up in gear you picked up a tenth in ET at the drag strip...3.55 - 3.91 -4.10 - 4.30 -4.56.
    The car's that didn't pick up a tenth usually needed a little larger carb to take advantage of the steeper gear...
    For a street car that doesn't see hi-way speeds a 3.91 - 4.10 is a fun gear ratio to have .
    There is a noticeable difference between seat of the pants feel between 3.23's and 3.55's. IMO
    For a stone stock 440 I'd use 3.55's
     
  10. dantrap

    dantrap Well-Known Member

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    I have used 3.91s in my old 68 beeper with a mostly stock 440 and 727 with a 3k conveter. The car had a 275-60-15 M & T street tire and was great to zip around town with. That 440 had 915 heads, the old .509 hyd cam a edel. torker with a 750 DP holley. It was a very mild setup, highway runs were ok. The RPM is liveable unless your really pushin the speed limit for a long distance.
     
  11. george68hemirr

    george68hemirr Well-Known Member

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    3.23=gas mileage
    4.56=get there in a hurry in a short distance
     
  12. moparcanuck

    moparcanuck Deceased, But not forgotton

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    I love my 3:23 and 28" tires: 2400RPM @ 60mph.:yes:

    Still has plenty of punch to burn the tires at a stop light too.:grin:
     
  13. 69 GTX

    69 GTX FBBO Gold Member FBBO Gold Member

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    I'd say 3.54 with oem height tires 3.73 with taller tires.
     
  14. 67 B-body

    67 B-body Well-Known Member

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    My 69 RR had 4.10:1,,,, I think it ran around 3,500 rpm at 55 mph. 60 was around 3,700 I think...
     
  15. tallhair

    tallhair Rufus "Mod-hair" Firefly Staff Member

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    When I drive a stock 68-70 b body with a 440 magnum and 3.23's 'no guts' is not a term that comes to mind. Higher numerical gears are definitely a lot of fun but for every numerical increase in gear ratio makes it that much less of a longer distance interstate cruiser, unless you like going 55 and me and Sammy don't.

    If you know the RPM you would be comfortable with on the interstate or highway just find one of the tire size/gear ration calculators and experiment to get the setup you think you could live with the easiest and have the most fun with.

    I've run 3.91s and 4.10's and they are a blast but you are taching at 55-60 .. I've also run 2.76's and 3.23's which are great for the long hauls and even with the 2.76's the car had plenty of torque to handle the those gears and were a blast on the freeway. Another thing to consider is getting a second chunk w/ 2.76's and just swap if you are going to go to a longer distance car show or whatever that's several hundred miles away. It's not hard to change them esp after you do it a time or two.
     
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    • 68GTX4SPEED

      68GTX4SPEED Well-Known Member

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    • tallhair

      tallhair Rufus "Mod-hair" Firefly Staff Member

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      That one is my personal favorite but the needle on the tach is off (like the originals :) ) so pay attention to the number posted over it.

      I also love it cause it tells you the tire height of a given tire profile .. just toggle back and forth
       
    • lewtot184

      lewtot184 Well-Known Member

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      i did some gear changing/track testing some yrs back with my '69 r/t. this was a basically stock engine with a 6-pak, automatic. i tried 3.23, 3.55. 3.91. the car was quicker with the 3.23. there wasn't any gain in performance with the lower gears. i wondered why. took the car to a chassis dyno and peak power was around 4300rpm and stayed relatively flat to 5300rpm when power fell off a cliff. i just so happens that with the 3.23 my trap rpm was 4300! then i thought about the fact that the 4bbl magnum engine has a peak power rating at 4600rpm and i think the 6-pak was 4700rpm. since then i have taken the 6-pak off the r/t and installed the original intake and carb. i believe peak power with the stock combo is 4500-4700rpm at it's best. i actually think the 4bbl combo would work fine with a 2.94 because there is so much low and mid-range torque.
       
    • hunt2elk

      hunt2elk FBBO Gold Member FBBO Gold Member

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      You guys realize this was a 1 post wonder from 4.5 years ago?
       
    • tallhair

      tallhair Rufus "Mod-hair" Firefly Staff Member

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      hahahahaha .. it happens once in a while. What fooled me was a lot of the guys posting in 09 are still here. Still good info though so hope it helps someone and that question is timeless
       
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