Highway driving....RPMS

Engine, Trans & Driveline

  1. Bad Sport

    Bad Sport FBBO Gold Member FBBO Gold Member

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    I would have been more righter, lol, if I hadn't left out a sentence.
     
  2. HEMI-ITIS

    HEMI-ITIS STREETER on LI FBBO Gold Member

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    -37.jpg -48.jpg -50.jpg -51.jpg
     
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    • 451Mopar

      451Mopar Well-Known Member

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      My '69 Coronet was an A-833 4-speed, 3.54:1 Dana and 27" Diameter (255x60x15) tires.
      75 MPH would have been 3,300 RPM.
      Installed the LGT-700 (Keisler SS-700) 5-Speed transmission that has 0.68:1 Overdrive, Now 75 MPH is 2,243 RPM.
      http://legendgt.com/Products/lgt-700/

      The Passion Performance A-855 5-speed has a 0.70:1 overdrive ratio
      The TKO-600 can be had with a 0.64:1 Overdrive ratio, not sure about swap kits?
       
    • 69sunfireGTX

      69sunfireGTX Well-Known Member

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      the TKO-600 has 2 options for the overdrive ratio's. .64 OD or the .82 OD The .64 is a long throw compared to the .82
       
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      • threewood

        threewood Well-Known Member

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        I have 3.55 rear gears, 295/50-15 tires (26.6" tall) and at 65 mph I am turning 3100 rpms. 70mph is about 3250 rpms.
         
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        • 747mopar

          747mopar Well-Known Member

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          Yeap, that's exactly where I was with 3:55's before the 6 speed.. now it's 1,800-1,900 rpm at 80 mph lol.
           
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          • koosh

            koosh Well-Known Member

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            Ok guys, FINALLY warm enough to get under car and mark driveshaft....it turned 3.5 revolutions, to 1 revolution of the tire...BOTH wheels rotated forward.....
            So, I have 3.55 gears? Suregrip?
            If I want highway cruising, do I want 3.23s, or 2.96s?
             
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            • 33 IMP

              33 IMP Well-Known Member

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              You have a suregrip.
              3.55 gears are a good compromise gear, biased toward street performance, 3.23 is the best compromise, decent acceleration, decent revs on the highway. 2.76 or 2.93 are freeway flyers, but off- the-line will suffer. You have to decide what you want, how you plan to use the car, and what compromise you can live with.
              I also believe that two series gears are hard to find used, and impossible new, but I may be wrong about that.
               
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              • Dennis H

                Dennis H FBBO Gold Member FBBO Gold Member

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                Jesus Chrysler this is painful. Like described, plant your right foot and count the streaks. Don’t like laying under the car with a crayon, etc. i have never known or cared about offset or tire diameter. Put a Tremec in and be done with it. 1935 @ 65 w/SST.
                 
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                • koosh

                  koosh Well-Known Member

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                  Send me over a blank check, I'll put the Tremec in.....not all of us are Rockafellers....
                   
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                  • koosh

                    koosh Well-Known Member

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                    Thanks......I'm finding that out about the 2 series gears....cant find em.....probably will have to suffer with 323, has to be somewhat? Better than 355
                     
                  • Dennis H

                    Dennis H FBBO Gold Member FBBO Gold Member

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                    That’s me! How did you know.
                     
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                    • moper

                      moper Well-Known Member

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                      There's not much of a difference between .23 and .55. If you consider the engine "screaming" (with the understanding that a: it's a car from an earlier era and it will be noisier and b: the 383 is a short stroke, long piston engine and designed to be driven for hours at 3500rpm) then you need to save up and change the transmission. I'd suggest an A833OD as a good alternative that is lower cost and basically bolt in, give or take. You need one out of a truck or van. Have the bellhousing hole enlarged for it, and bolt it in. You'll need to take care with the shift levers and adjustments of the rods, but it's an OD drop in that will make a difference for less than a second 8 3/4 pig.
                       
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                      • koosh

                        koosh Well-Known Member

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                        An overdrive tranny is cheaper than a set of rear gears?
                         
                      • 33 IMP

                        33 IMP Well-Known Member

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                        The difference between 3.23 and 3.55 is around 9%, so 3000rpm with 3.55 goes to around 2750.
                        I think what moper is saying is that a factory overdrive 833 is a lot cheaper than a five speed tremec.
                        The difference between 3.55 and 2.93 is around 17.5% so 3000 rpm goes to 2450.
                         
                      • koosh

                        koosh Well-Known Member

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                        Ahhh......ok thanks
                         
                      • koosh

                        koosh Well-Known Member

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                        So......"383 is a short stroke, long piston engine and designed to be driven for hours at 3500rpm", your saying this is normal and ok? Then......maybe I should just leave things be.....its been long time since I had my 1st RR, and just dont remember the motor "screaming " that much WAY back then! Lol
                         
                      • moper

                        moper Well-Known Member

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                        I'm saying they were sold with a warranty in everything from school busses and trucks to family wagons to performance cars - and they all had the same lower ends. But the cars (and owners of the time did not consider fuel economy as a big deal, and the transmissions only had three speeds. My '65 A body had a slanty, with a 3.23 and 13" wheel and tire package. 50 years after it was "new", I was bombing it down the highway at 75-80 with no tach. Not a big deal. My old 2bbl 383, with 85K original miles, a cam, 4bbl, and 175hp nitrous plate ran down the road at 4500+ for over an hour quick frequently because I was dating a girl at a college 150 miles away.
                        As long as the oil pressure reads fine (assuming a gage not a light), and the temps don't creep up, the highway rpm is not a significant issue. You won't shorten the service life by 50% or anything. You will use more gas, in the long run it will wear out a smidge faster, and it will be noisier in the cabin. But you won't hurt it if it's good to begin with.
                         
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                        • INTMD8

                          INTMD8 Well-Known Member

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                          3.55's wouldn't bother me at all with no overdrive.

                          Once drove a 78 Trans Am from California to Illinois, 4 speed with 3.73's holding it at 5000rpm through every tank of gas.

                          That didn't bother me (or the car) either :)
                           
                        • HEMI-ITIS

                          HEMI-ITIS STREETER on LI FBBO Gold Member

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                          4:10 and 31 inch tall tire I'm about 3k RPM @ 60mph.

                           
                          Last edited: Apr 7, 2019
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