Highway driving....RPMS

Engine, Trans & Driveline

  1. R/T Boy 67

    R/T Boy 67 Well-Known Member

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    If you have an open diff, with both tires off the ground, turning in opposite directions, you will be waiting a long time for the drive shaft to make a revolution.
     
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    • 65moneypit440

      65moneypit440 Active Member

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      GV is going in, 3000-mile road trip coming up. 3.23 gears, 235/70/15. 79EFCB08-7CEB-42EE-ACC6-5782D38A1E93.jpeg
       
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      • Dennis H

        Dennis H FBBO Gold Member FBBO Gold Member

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        Love that Tach,

        Rocky
         
      • Don Frelier

        Don Frelier FBBO Gold Member FBBO Gold Member

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        So your tach reads around 3,500 rpm at 65?
        With 3.23 gears and 235/70 tires I would expect around 2,750?
        That's a fairly large discrepency, sure the tach and ratio are right?
        Speedometer is accurate as well?
         
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        • Fran Blacker

          Fran Blacker FBBO Gold Member FBBO Gold Member

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          You sure you have 3.23's in there? Looks like 3.73's, ran 3.54's 3000 at around 65 mph.
           
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          • Don Frelier

            Don Frelier FBBO Gold Member FBBO Gold Member

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            If the tach and speedo are correct, it's probably higher than 3.73.
             
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            • BSB67

              BSB67 FBBO Gold Member FBBO Gold Member

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              And I would hope that your WOT shift point is a bit higher
               
            • Dennis H

              Dennis H FBBO Gold Member FBBO Gold Member

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              My 440 stops pulling at 4850 per the chassis dyno. No reason to go upstairs.
               
            • BSB67

              BSB67 FBBO Gold Member FBBO Gold Member

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              Factory with the cast iron intake go 5200.

              What was your peak hp, 4300? Smaller than factory cam?
               
            • Dennis H

              Dennis H FBBO Gold Member FBBO Gold Member

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              Misspoke i guess. Max power at 4850. I’ll dig up the dyno sheet. 30 over slightly warmed up Comp Cam.
               
            • BSB67

              BSB67 FBBO Gold Member FBBO Gold Member

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              That makes more sense. What intake?
               
            • Dennis H

              Dennis H FBBO Gold Member FBBO Gold Member

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              Edelbrock RPM 850 Demon at the time. 415 rwhp.
               
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              • 65moneypit440

                65moneypit440 Active Member

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                I’ve double-checked the tach, checked the speedo with other cars and using the mile marker/clock method, and saw the “3.23” on the ring gear myself. You’re right, it doesn’t add up. I just want it to come down.
                 
              • Don Frelier

                Don Frelier FBBO Gold Member FBBO Gold Member

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                is the tach possibly set up for a 6 cylinder?
                8/6 = 1.333 which is equal to about how far off I think your tach is.
                Just an idea.
                Does it have any dips switches or jumpers, see if you can get a manual?
                I have 3.23 in both my 66's and I wouldn't say they scream at highway speeds.
                 
              • 33 IMP

                33 IMP Well-Known Member

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                Please don't take this wrong,it's NOT meant as an insult, but did you count the teeth on the ring and pinion, or jack the car up and recheck the ratio?
                The numbers on your tach and speedo correspond to a 4.10 gear, and if that's what you have, I can understand you think it's screaming.
                I checked with the Wallace calculator, if you have 3.23 and 28" tall tires, 3500 should get you 85 plus mph. 65mph should be around 2700, not 3500.
                For what it's worth, I have a 4.10 geared car with 28" tires, and it runs almost exactly 3500/65mph.
                 
              • 65moneypit440

                65moneypit440 Active Member

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                Ok, here’s the deal (relating to post 42). My 904 is a 1987 “non-locking” unit, so the torque converter is still slipping in high gear. I’m told it can’t be corrected easily in my old car. Neither can the GV be installed without more floor-pounding and pipe-bending than I feel comfortable with. The overdrive is going back to El Cajon, and the tach is coming out. Thanks for your comments Don, Dennis, Fran, and 33 Imp, ‘preciate it!
                 
              • Cojohnso1

                Cojohnso1 Well-Known Member

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                3.54:1 is solid all around gear ratio for street. I have 28" on rear. And it hums great. About 2800 @ 60 MPH. The 440 is not super fast thru the gears. Doesn't really start pull decent until 70+. Would love that new Passon 5 speed with .70 OD with a set of 4.10 or 4.56 rear gear? Then the BB is in its power range quicker. Bet it would shave a near full second off 1/4 time. High 13 to high 12?
                 
                Last edited: Apr 13, 2019
              • 66 Sat

                66 Sat Well-Known Member

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                Well after reading this thread I finally got around to checking my ratio this morning. Jacked the rear up, 3.23 and a sure grip! I thought I had a 2.93 open rear. That explains why it hooks up so well out of T junctions.
                 
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