Gear Ratio and RPM deciding on gears

Mopar General Discussions

  1. 340inabbody

    340inabbody Well-Known Member

    Messages:
    244
    Likes Received:
    54
    Joined:
    Jan 31, 2018
    Location:
    Arizona
    Local Time:
    10:06 AM
    Guys looking to decide over a 3.55 or 4.11 still. Have been reviewing my old threads as well as others. Ran some numbers and wanted bounce off conclusions from this and if I am missing anything. I used the Spicer calculator. Red dotted lines are approximated power band.

    1. My 2.71 never makes it into the power band!
    2. The 4.56 could hit my rev limiter just over 100MPH say if I was doing the 1/4 mile
    3. Not a huge difference between the 3.55 and 4.11 at cruise 70 MPH

    What is a reasonable RPM at cruise 65ish for a 340?
    Am I missing anything? Does load or type of transmission alter the plots?

    Thanks

    IMG_4618.jpg
     
  2. yellow rose

    yellow rose Doctor of Thinkology.

    Messages:
    20,003
    Likes Received:
    16104
    Joined:
    Jun 19, 2015
    Location:
    Living on the razors edge
    Local Time:
    9:06 AM
    I run 4.56's and a 27 inch tire.

    Need to know more about the combo.

    It's mostly about what you can live with, and the rest of the car.
     
    • Agree Agree x 2
    • Alaskan_TA

      Alaskan_TA Well-Known Member

      Messages:
      5,263
      Likes Received:
      3425
      Joined:
      Nov 12, 2004
      Location:
      PA
      Local Time:
      12:06 PM
      Road use?

      Track only?

      Details matter. ;-)
       
      • Agree Agree x 2
      • GreyWizard

        GreyWizard Well-Known Member

        Messages:
        278
        Likes Received:
        218
        Joined:
        Jan 28, 2018
        Location:
        Colorado
        Local Time:
        10:06 AM
        I have 26" tall rears and 3.55 gears on my Dart. It is plenty loud at 65-70 mph. I would not want to drive very far on the highway. I have thought about 3.73s to improve strip performance but would be reluctant to go far past that.

        Good luck.
         
        • Agree Agree x 1
        • 318willrun

          318willrun Roadkill '80 D150

          Messages:
          12,874
          Likes Received:
          12836
          Joined:
          Sep 13, 2013
          Location:
          I'm here
          Local Time:
          11:06 AM
          well, all we have to go on so far is "70 mph". IF his car needs to travel 70 mph for distance, I'd go 3.23's max, my opinion
           
          • Agree Agree x 2
          • Like Like x 1
          • 318willrun

            318willrun Roadkill '80 D150

            Messages:
            12,874
            Likes Received:
            12836
            Joined:
            Sep 13, 2013
            Location:
            I'm here
            Local Time:
            11:06 AM
            100% agree. The back of my neck gets tense when it sounds like I'm in 2nd gear at 60 mph, and passengers ask "are you in drive?".
             
          • QuickDart360

            QuickDart360 Well-Known Member

            Messages:
            1,033
            Likes Received:
            341
            Joined:
            Apr 5, 2014
            Location:
            San Antonio
            Local Time:
            11:06 AM
            I went with 3.91's from 3.55's. Have not yet driven my car yet but my rear tires are 28". May not feel alot of rpm difference maybe but take offs will be better I hope!!:steering:
             
          • GreyWizard

            GreyWizard Well-Known Member

            Messages:
            278
            Likes Received:
            218
            Joined:
            Jan 28, 2018
            Location:
            Colorado
            Local Time:
            10:06 AM
            Rear gears quickly separate the drivers from the trailered cars.
             
            • Like Like x 2
            • Agree Agree x 2
            • 340inabbody

              340inabbody Well-Known Member

              Messages:
              244
              Likes Received:
              54
              Joined:
              Jan 31, 2018
              Location:
              Arizona
              Local Time:
              10:06 AM
              I want a hot street car that I can take on the track a few times a year at most since I don't have a lot of money to replace parts etc. But I would like to be able to ride a decent torque curve around town and the torque of the 340 starts above 3000 probably more like what I show in the graph at 3800. Wouldn't 4.11's have more torque around town than a 3.55? I don't plan on leaving the Phoenix metro area and tour with. I DO want performance and the 2.71 I have is a dog with the torque converter as is. I plan on working with Lenny AFTER I get the rear ratio in. There is always a split on what rear gear ration is best. All I know is I have a 904A 3 speed trans that idles at 35MPH lol which is not good.
               
            • 340inabbody

              340inabbody Well-Known Member

              Messages:
              244
              Likes Received:
              54
              Joined:
              Jan 31, 2018
              Location:
              Arizona
              Local Time:
              10:06 AM
              Oh and 70MPH is worst case cruise for the sake of comparison here.
               
            • 318willrun

              318willrun Roadkill '80 D150

              Messages:
              12,874
              Likes Received:
              12836
              Joined:
              Sep 13, 2013
              Location:
              I'm here
              Local Time:
              11:06 AM
              well, if you going to be 55 mph or under, then go 4.11's. I don't know what you call a dog because some think a 1.8 60 ft time is a dog and others think a 1.8 is a race machine, but if it's a lazy pig that won't cross the street with 2.71's, then you probably have another issue.
               
              • Like Like x 1
              • marksmopars

                marksmopars Well-Known Member

                Messages:
                323
                Likes Received:
                91
                Joined:
                Nov 30, 2011
                Location:
                Minnesota
                Local Time:
                11:06 AM
                I have a 340 runs pump gas and my power band is 700 rpm higher than your chart. My car is stock 3.53 and I can cruse 70 in it but not 80. I wouldn’t recommend 4.11 on the freeway for any distance.
                 
                • Agree Agree x 1
                • 340inabbody

                  340inabbody Well-Known Member

                  Messages:
                  244
                  Likes Received:
                  54
                  Joined:
                  Jan 31, 2018
                  Location:
                  Arizona
                  Local Time:
                  10:06 AM
                  Yeah the power band is a guess and every set up different. What kind of rpm are you at 70mph?
                   
                • MOPAROFFICIAL

                  MOPAROFFICIAL Well-Known Member

                  Messages:
                  4,805
                  Likes Received:
                  3819
                  Joined:
                  Jun 1, 2016
                  Location:
                  Beach
                  Local Time:
                  9:06 AM
                  3.73's
                   
                • RustyRatRod

                  RustyRatRod Weenie idiot loser. FABO Gold Member

                  Messages:
                  58,022
                  Likes Received:
                  28124
                  Joined:
                  Jun 7, 2010
                  Location:
                  Georgia
                  Local Time:
                  12:06 PM
                  Yeah I was gonna say either this ^^^^^ or 3.91s.

                  HOWEVER, you STILL have not answered the question asked. WHAT'S YOUR ENGINE COMBO? Are we just "supposed" to know somehow? The cats knocked off my crystal ball and broke it a long time ago. Are we supposed to remember YOUR combo from another thread? Fat chance for my "old butt". PLEASE enlighten us if you want an answer remotely "accurate".
                   
                  • Agree Agree x 1
                  • MOPAROFFICIAL

                    MOPAROFFICIAL Well-Known Member

                    Messages:
                    4,805
                    Likes Received:
                    3819
                    Joined:
                    Jun 1, 2016
                    Location:
                    Beach
                    Local Time:
                    9:06 AM
                    I agree. OP!
                    But ill say in general, with a 3.31 stroke that 3000-to 3800 is typical. Though in the next lane... the guy thinks 4200rpm down the freeway is where its at.
                     
                    • Like Like x 1
                    • 340inabbody

                      340inabbody Well-Known Member

                      Messages:
                      244
                      Likes Received:
                      54
                      Joined:
                      Jan 31, 2018
                      Location:
                      Arizona
                      Local Time:
                      10:06 AM
                      Sorry. My question was regarding the plots I made and conclusions rendered. The combination is a 340 dont have the CAM specs or compression specs as I got the engine without any docs. Its an aggressive cam run by an MSD 6AL steal stock heads Holley 650 double pumper with mechanical advance (I know) Mopar high rise intake and apparently a stock 904A trans. The current rear is a peg leg 2.71 in which I have a Spicer Sure grip 27 spline. I have it timed at 19 deg at idle 31 all in with a slow curve due to detonation. This detonation is partly due to the luging combo of a shitty rear gear 2.71 and and a converter (unknown stall). This is everything I know about the combo.
                       
                    • 273

                      273 Well-Known Member

                      Messages:
                      2,940
                      Likes Received:
                      731
                      Joined:
                      May 14, 2012
                      Location:
                      Ontario
                      Local Time:
                      12:06 PM
                      What mph are you doing at the track, and what’s your combo ??

                      but as a guess if you don’t mind the crusin rpm of 4:10 go with that.
                       
                    • toolmanmike

                      toolmanmike FABO Staff Staff Member FABO Gold Member

                      Messages:
                      45,791
                      Likes Received:
                      29894
                      Joined:
                      Jan 18, 2006
                      Location:
                      Iowa
                      Local Time:
                      11:06 AM
                      Last edited: Jan 17, 2020
                    • MOPAROFFICIAL

                      MOPAROFFICIAL Well-Known Member

                      Messages:
                      4,805
                      Likes Received:
                      3819
                      Joined:
                      Jun 1, 2016
                      Location:
                      Beach
                      Local Time:
                      9:06 AM
                      5.13's
                       
                      • Thanks! Thanks! x 1
                      • MOPAROFFICIAL

                        MOPAROFFICIAL Well-Known Member

                        Messages:
                        4,805
                        Likes Received:
                        3819
                        Joined:
                        Jun 1, 2016
                        Location:
                        Beach
                        Local Time:
                        9:06 AM
                        Op should pour a bottle of slick50 in the ole chrome valve cover and go n do burnouts into a brick wall somewhere over the rainbow.
                        Sciencing out a cruise rpm is mental masturbation
                         
                        • Like Like x 1
                        • jas0162

                          jas0162 Well-Known Member

                          Messages:
                          477
                          Likes Received:
                          292
                          Joined:
                          Apr 23, 2014
                          Location:
                          kansas
                          Local Time:
                          11:06 AM
                          3.91 or 4.10 gears are no fun at all if you use the stock non overdrive trans and do any freeway driving. If you just run around town or race they are great. 3.23 is the best compromise in my opinion. If the car is a “dog” with 3.23 gears, a set of deeper gears won’t make that much difference.
                           
                          • Agree Agree x 2
                          • toolmanmike

                            toolmanmike FABO Staff Staff Member FABO Gold Member

                            Messages:
                            45,791
                            Likes Received:
                            29894
                            Joined:
                            Jan 18, 2006
                            Location:
                            Iowa
                            Local Time:
                            11:06 AM
                            Mental masturbation! :rofl::rofl::rofl:
                             
                            • Thanks! Thanks! x 1
                            • RustyRatRod

                              RustyRatRod Weenie idiot loser. FABO Gold Member

                              Messages:
                              58,022
                              Likes Received:
                              28124
                              Joined:
                              Jun 7, 2010
                              Location:
                              Georgia
                              Local Time:
                              12:06 PM
                              Every now and again he "hits the nail on the head". LOL
                               
                              • Agree Agree x 2
                              • 273

                                273 Well-Known Member

                                Messages:
                                2,940
                                Likes Received:
                                731
                                Joined:
                                May 14, 2012
                                Location:
                                Ontario
                                Local Time:
                                12:06 PM

                                How are deeper gears not gonna help if your car is a dog ??

                                what would it take if not gears to dial in your combo ?
                                 
                              • RustyRatRod

                                RustyRatRod Weenie idiot loser. FABO Gold Member

                                Messages:
                                58,022
                                Likes Received:
                                28124
                                Joined:
                                Jun 7, 2010
                                Location:
                                Georgia
                                Local Time:
                                12:06 PM
                                Not talkin about the OP here, BUT.........

                                I know I've preached it till I am blue in the face. People come on here wantin to know "what gear" or "what converter" is best. They have (for example) a 340, 240-260 @ .050 cam, all the goodies and then curl up in the fetal position like a little sissie when I say "3600-3800 stall and 4.30 gears".

                                If you're gonna build one with "all that" up front than "what's out back" needs to match.
                                 
                                • Agree Agree x 6
                                • Like Like x 1
                                1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
                                  By continuing to use this site, you are consenting to our use of cookies.