Would like input on rear gearing

Engine, Trans & Driveline

  1. Odmark91

    Odmark91 Well-Known Member

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    Hello. Im pulling my differential to install a limited slip, and also maybe put another gear set in there.

    The engine is a 505 Stroker dynoed to 587 horsepower and 850 Nm (627 lb-fts) with a A833 4-speed behind it and it sits in a 1964 Dodge Polara 2 door. And it sits on 25 inch tall tires.

    The previous owner claimed it had 3.23 gears or something like that but im not sure, do you think that would be a good gearing for the street? I very rarely drive highway.
    I have a set of 4.10 gears on the shelf but i feel like that will be to much with this engine setup?

    What gears would you recommend for the best all around use, street, occasional racing etc.
     
  2. MoparLeo

    MoparLeo NRA PATRON LEVEL LIFE MEMBER FBBO Gold Member

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    • 69 GTX

      69 GTX FBBO Gold Member FBBO Gold Member

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      I would stay with 3:23s, with that much torque you don't need steep gears.
       
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      • Odmark91

        Odmark91 Well-Known Member

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        Thank you, i was looking for a calc like that but couldnt find one. 57 mph at 2500 rpm with 3.23 gears sounds way better than 3300 with 4.10 gears. If my calculations are correct.

        69 GTX: Yeah i think ill stick with the 3.23, if thats really whats in it. I need to check.
         
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        • biomedtechguy

          biomedtechguy Accelerati Rapidus Maximus FBBO Gold Member

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          My 3.54 gears and 25.5" diameter tires netted 3,500 RPMs at about 72 MPH which was "ok" but now I turn about 2,750 at that speed and it's much more pleasant.
          Unless you are looking for max acceleration AND have tires that would grab vs smoke, 3.23 is fine.
          Having said that, I got my new number I referenced by swapping in a Passon Performance 5 speed and a 4.10 for the 3.54.
          I'm likely to go back to the 3.54 when I install a stroker motor I'm putting together, but I am looking for the quickest 1/4 mile times.
           
        • 747mopar

          747mopar FBBO Gold Member FBBO Gold Member

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          I'd stick with the 3.23's, it isn't like you need a lot of help getting the car moving with that much torque lol. 3:55's is the lowest I'd ever go for a street car, great all around gear but does get annoying after a bit on the freeway.
           
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          • 91r/t

            91r/t FBBO Gold Member FBBO Gold Member

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            My 68 Charger has a similar stroker with the 4 speed and I run 3.55's in the rear with a 28" tire which will net similar RPM's as your combo will. It is way more pleasant to drive than when I had the 3.91's in the rear and screamed everywhere on the thruway. It also helps me hook up as the car before with 3.91's would burn tires at 45-50mph which was pointless. Fun for a bit but better now with the taller gear for sure! You will enjoy it way more leaving it as is.
            :thumbsup:
             
          • Nevada dan

            Nevada dan Well-Known Member

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            with that occasional race you might be disappointed not getting out of third gear in the quarter mile with the 323
             
          • PurpleBeeper

            PurpleBeeper Well-Known Member

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            I'm with these guys, 3.23, 3.54, 3.55
             
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            • Odmark91

              Odmark91 Well-Known Member

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              Im gonna pull the 3rd member and see whats in it, if it is 3.23 or lower i will keep it, but if its higher then 3.23 i think i will buy a 3.55. Thank you all for your inputs!
               
            • Photon440

              Photon440 FBBO Gold Member FBBO Gold Member

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              You won't need to pull it. Just spin the pinion and see if it rotates 3.23 times for one tire rotation (assuming sure grip).
               
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              • 451Mopar

                451Mopar Well-Known Member

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                The 3.54/3.55 ratio works good in most case. The actual tire height will matter too.
                With the big engine and short tires the 3.23 gear will be better if you do much highway driving.
                 
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                • 383man

                  383man Well-Known Member

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                  Much depends on how tall of a rear tire you plan to run. I run 4.30's in my 63 with my 493 I built. But I run 30" tall rear tires so I turn around 3000 to 3200 rpm in the 60 to 65 mph area and thats fine with me. I have driven it 90 miles at 60 to 65 mph on the highway. But I also race my car in Nostalgia Super Stock sometimes as I drive it to the track and race in full street trim through the full exh. I can tell you I feel that I could drop to 4.10's or 3.91's and go just as fast as the car just feels like it may go faster if I drop my trap rpm a little. But if you run a 25" tire heck 3.23's or 3.55's is what I would consider with a tire that short. Good luck , Ron
                   
                • bm02tj

                  bm02tj Well-Known Member

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                  You need to look at the curve for the motor as well
                  drive in third and do the calculation to see what it will be in fourth and gear ration your calculation give you then you have two points of reference to help choose

                  A-833 Transmission Gear Ratios 1st 2nd 3rd 4th
                  6-cyl (also 64-65 273, 74-75 318) 3.09 1.92 1.40 1.00
                  Fine-spline V8 (most pre-1971) 2.66 1.91 1.39 1.00
                  Coarse-spline V8 (1966-70) 2.65 1.93 1.39 1.00
                  Coarse-spline V8 (1971-74) 2.44 1.77 1.34 1.00
                  Road Race T/A; most 1971-74 fine spline 2.47 1.77 1.34 1.00
                  Overdrive (mid-1970s and newer) 3.09 1.67 1.00 0.73
                   
                  Last edited: Mar 14, 2021
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                  • Should be playing golf

                    Should be playing golf Active Member

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                    Compromise: Basically stock 440, A-833, 3:54 rear gears, 295/55/15 MT ET Street SS (28" tall), = 60mph @ 2500 rpm and.........12.1@109...I'll stick with it!:thumbsup:
                     
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                    • Barry Woodyard

                      Barry Woodyard 426 Woody FBBO Gold Member

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                      390 or 355 would be good gear for street. Don't need any more with that much Torque
                       
                    • Odmark91

                      Odmark91 Well-Known Member

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                      It had 3.23 gears in it, im gonna keep them for now and drive the car this summer, and then make a desicion next winter if im gonna keep them or maybe install a lower gear.
                       
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