Ordered a gear vendor, help with deciding gears

Mopar General Discussions

  1. rumblefish360

    rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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    Now that is an awesome example with the particulars you need to know.
    @DesertRat , do you know the OD’s final gear ratio?
     
  2. RogerCox

    RogerCox Well-Known Member

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    Sorry man! So many numbers to try to keep track of haha

    So will be running cobra Gt tires 80% of time and nitto 20% when weather is good.

    Cobra size: 295 50r15 (26.6” tall)
    Nitto size: 325 50r15 (27.8” tall)

    gear vendor ratio is .78 is what I am reading.
     
  3. rumblefish360

    rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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    Well now you have the numbers to the math minus torque converter slip for the automatic cars.

    .78 X gear ratio = final drive ratio
    Final drive ratio by tire diameter for cruise rpm.
    Go here and use the correct link for the calculator you need.
    Wallace Racing - Automotive Calculators
     
  4. DesertRat

    DesertRat FABO Gold Member FABO Gold Member

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    Yes the .78 is the number. Some folks don't think its enough but for me it worked out in my 67 notch. The one thing I did to mitigate the converter slip is go with a lock-up converter but after driving it a year I had the transmission shop remove the lock-up feature. The car is much more driver friendly with a little converter slip and it only cost me 100 rpm. I now cruise at 70 MPH @ 2400 RPM. My motor is real short on torque, builder mistake on me:-( But for a 408 it will work fine.
     
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    • chinze57

      chinze57 Push Button tranny and a Slant 6 that'll never die

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      The reason I am considering getting one is that I have a 64 with the Pushbutton trans. I want to keep the pushbuttons because they’re very unique, which limits my transmission choices. I do a lot of driving on the freeway, so having better acceleration with higher gears, and then being able to drop my Rpms at higher speeds is valuable to me.
       
    • TrailBeast

      TrailBeast AKA Mopars4us on Youtube

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      My friend Mike and I put one in his car and we had to cut out and raise a section under the bench seat 1.5 inches for the main gear section so the driveshaft angle was where it was supposed to be.
       
    • jos51700

      jos51700 Green Bearing thread connoisseur

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      Figure out where peak torque is on your car (I.e. dyno).

      Figure out how fast you want to run on the freeway.

      Pick the deepest rear gear as close as you can to make the two above coincide in top gear. You'll need your tire size and calculators for this are all over the net.

      It really is that simple.

      Maybe someone else covered it, I ain't reading all these posts.

      Example. Peak torque 2500 RPM.
      Freeway speed 80mph (you's in Montana an alla that).

      From their website:
      Overdrive is 0.78.
      So by the chart, the gear in red will behave like the gear in black.
      Dodge 3-Speed Auto - Gearvendors

      So with this calculator, 3.23 is your bingo (I just picked a tire size, Your mileage will, literally, vary)
      Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio

      Switch to 3.55's, and you're cruising at 2800.

      Compare this to a true six speed with double-over, and you'll see why people don't like the GV unit.
       
      Last edited: Feb 20, 2021
    • RogerCox

      RogerCox Well-Known Member

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      So with my t

      So with my tire (26.6”), 373 gears I would be at 2750 rpm at 75mph. Not terrible, could go 355 but I think I’ll do 373 to get more acceleration.


      i agree can’t compare it to a 6 speed, but I already have the 727 trans, so I’m thankful for the option.

      Thanks for the help guys
       
    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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      Ok so I put most of your comments from page 1 into one place, so I don't get confused by what others have said. And then I will comment in blue.Keep in mind that I'm just a guy with a calculator, that happens to have a GVod.
      I'm gonna post it out as I go, on account of my computer likes to lock up and loses the draft when it does.
      Have you given thought on how to fit those 315s into the Duster tubs?
      I'm not understanding this comment; so I'll take a stab at it' . Sensitivity at tip-in is always one of:
      1) too much low-rpm timing, or
      2) primaries that are too big, or
      3) too small a rear gear, or
      4) a spastic right foot, or
      5) some combination of the above.

      Oh yeah, yur on the right track.
      But I see two things in your thinking that I can't agree with;
      1) You have a 408, and
      2) on street tires, that
      3) in a Duster weighs practically nothing to a 408

      Ok so with a 408, a 727, a modest stall, on 295 Cobras, in a duster ..... is a recipe for tirespin......... no matter what rear gear you run. And there is NO CHANCE to split second and third. I mean you can but there is NO POINT IN A STREETER
      Lemme explain
      Your 727ratios are 2.45-1.45-1.00 adding the .78 GV ratios in Red I get
      2.45-1.91-1.45-1.13-1.00-.78od, your splits are
      .78- .76-.78-.88-.78
      So if you are in second-over and shifting to Third your Rs will drop to 88%, which, from 5500 is to 4840, is a drop of 660 rpm, which sounds good but here's the deal; with street 295s and 3.23s, that comes at 85 mph, and in all likelihood your tires will still be spinning. Soooooooooooooo what advantage is there to having the GVod in this instance? Answer; I hope you are somewhere that the coppers ain't. Remember what Rusty said? So that's strike one.

      Strike two for splitting is;.
      Between First and Second the splits are very nice and tight, a sucked out 318 would love it, for all the reasons you would think.
      But will your 408 love it? If your tires are spinning in first on the split, then no. If your 408 spins the tires in second gear then no. I have had those Cobras behind my 367 and she spins them to long past 60
      If your 408 cannot roast 295 street Cobras to 60 mph. it is sick. So then, what advantage is the GVod in this instance? For splitting the big 408, IMO, nothing; certainly not anywhere near worth the buy-in.So that's strike Two.
      Strike three is this; The GVod cannot be backshifted under power. So when going from First-over or Second-over to the next non-over gear the power has to be interrupted while the unit out-shifts.

      End of the bad stuff.
      Here comes the good stuff
      With 3.23s your trip to 65mph cruising speed could end at 3000/zeroslip, maybe 3300 under power in Second over. Dropping into Third-over at 2060@zero slip. Do the math. That is a drop of 38% making the OD EFFECTIVE ratio to be .62. NOT .78 that everybody complains about. So then your shifts would be

      2.45-1.45-1.13-.78 That's very nice.
      There is no good reason to run 3.23s which do nothing but drop your rpm too low for most street cams, which will want 2400 down to 2200. But it is nearly impossible to give the engine the optimum timing to cruise at those rpms. 2400 is just barely doable with non-computer-assisted timing controls.

      So, to cruise 2400@ 65mph with 26.7" tires will take, surprise surprise; 3.73s for 65= 2400 in loc-up, up to 240 more at 10% slip. That, you can optimize the cruise timing for.
      So having settled on 3.73s, you now have a tire-fryer in second gear, to 65=4400@zero-slip, perhaps 5100, at 15% slip, on the tach. No GVod required.

      [/QUOTE]
      So now with the math done; lemme show you something;
      First; you gotta know that the TC has a hydraulic multiplier in it, by the way that it works. This multiplier, at WOT, can vary between 1.8 at zero mph, to perhaps 1.1 at 100 mph. It is like a Torque-Sensitive, CVT, with an overall ratio of 1.1/1.8=.61 or very close to a fourth automatic gear that does the bulk of it's work right on the starting line, but never actually quits.
      Suppose your engine makes 380 ftlbs at stall. Thru the trans (more math coming), that would math to 380 x1.8 x2.45 x3.23= 5413 ftlbs into the rear axles, at zero-mph. I guaranstinkingtee you the tires will spin. And as the rpm goes up the torque curve, the TC will lose some ratio, while the engine builds torque with rpm, and that will keep the tires spinning, until the power just kills them, all the way thru first gear.
      When she hits Second the Rs will drop from say 5800 to 3400, back into the fat part of the torque curve, say 410 ftlbs. And the TC ratio may have dropped to 1.3 or 1.2, so into the rear axles now, you get

      410 x1.25 x1.45 x3.23=2400 ftlbs just enough to keep those Cobras boiling. And as the engine climbs up the powercurve, those Cobras will never hook. Not in first, and not in second, unless you pedal it.
      So knowing this is possible
      IMO

      Forget the GVod, and leave the 3.23s in there.
      IMO
      Give them a chance at least.
      My 367 will bust those Cobras loose at 50/55 mph, with just a

      footstomp. I have no help from a convertor. My second gear ratio is 1.92 x 3.55=6.82.
      Your second gear ratio, from a footstomp will be close to 1.45 x3.23 x1.25=5.85, or about 14% less than my 6.82. But you have a 408 compared to my 367, so 11% more cubes, and your engine, at 50 mph will be doing 3700, to my 4280. Your's is on the rising side of the torque curve, while mine is on the falling side. I think your 408 will annihilate your tires worse than my 367..................... lol.
      3.23s will cruise 65=2640@ zero-slip. This is easy to work out the cruise timing for, which will offer the potential for max fuel-economy. This is also easy to work out the cruise-fueling for again maximizing your potential for fuel economy.
      And the best news is this; at 32mph on the 2-1 downshift, the Rs will rise to 4140 from 2450 in Second, which means going from sleeper mode, to batchit crazy instant tirespin. And first gear will go to about 50 mph@ 5720@15% slip. Those are nice street numbers.
      So,

      IMO,
      For your combo; I would leave it the way it is until you get your traction issues worked out. I mean don't get me wrong, I love blowing my tires off every chance I get, but the GVod is pretty much reserved to the final shift on the hiway. My lil 367 has plenty enough power to kill the tires easily to 65 mpg; (295s, Cobras or BFGs). Or even the 325/50-15 BFG Drag-radials I bough for the track. With street suspension, I get 2.2 to 2.4 60fts, and tirespin, they say to over93 mph. And my tach concurs.

      I cannot in my wildest imagination think that a 408 wouldn't better that; even with 3.23s.
      Jus trying to save you a ton of money.

      now, if you had a 318, that's a whole nuther story.
       
      Last edited: Feb 20, 2021
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      • Jesus Chrysler

        Jesus Chrysler Forgiving Sins Against Mopar Since 1983

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        passing fad going on 40 years?
         
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        • RogerCox

          RogerCox Well-Known Member

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          [/QUOTE]


          Awesome information thank you AJ.
          So basically no point in using 1st or second OD because the Cobras will just get roasted. On hot day here maybe the Nittos could stick better.

          so the only Benefit is getting from the Gv is just the 3rd OD on the highway.

          so could save the $3000 and just run 3:23 gears and be at 2900 rpm at 70.

          I would really like to maximize the power of my engine, I know traction will be a big issue but if I could get the tires to hook, wouldn’t a GV and 3:73 gears be much quicker?
           
        • RustyRatRod

          RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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          Some people say a certain 2000 year story is a passing fad. Course, that ain't me.

          But yeah, I'm just giving my opinion and reporting on things I've seen people who've had them say on this forum. Seen some pretty disappointed in the OD ratio and the floor mods....but mods are what hot rodding is all about. If you're gonna be a cry baby about that, there's always tiddly winks.
           
          Last edited: Feb 20, 2021
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          • RustyRatRod

            RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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            Sounds to me like you're exactly the person he needs to talk to in this case.
             
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            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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              Not on the street, well maybe, but you can't measure it lol. The GVod needs a power interrupt on the out shift. What you gain in, the more average power delivered, you will lose on the interrupt. Furthermore on the outshift, the GV does not shift instantly when you hit the button. So you have to anticipate it.
              I have a clutch so I hit the outshift button before I clutch it, then the GV outshifts while I'm selecting the next gear. IDK how fast I can shift, maybe .2 or .3 second, but the GV is always done before the power gets back on.

              For you, if you need more power down low, because your 408 is lazy down there, then just put a higher stall convertor in it.
              Or if the 408 is lazy down low on the 1-2 shift, either wring her out higher or again, install a higher stall. Like a 3800. When you shift into second, the Rs will drop to 1.45/2.45=59.2% So shifting at 5500, will get you 3255 into second. But shifting at 6000 will get you 3550.
              Whereas the 3800 will get you .. um 3800, anytime before about 3800/.592=6440.

              If you haven't driven this combo yet, save your cash. leave whatever gears are in the Dana in there, and just drive it for a few weeks. Let her tell you where she is weak, if weak she might be.

              But I gotta tell you another thing. For a streeter, in straight-line performance, there are only two times the rear gear makes a difference. They are;
              1) on the start line, and
              2) thru the traps.
              All the rest of the time you are just moving horsepower around.
              Since your 408, IMO cannot help but, at WOT, spin the tires all thru first gear, #1 is a bust.
              Since the 408 at WOT, is likely to still be spinning the tires at 65 mph, that's a bust too.
              Since the speed limit is 65 mph, trapping is sortof a bust.
              In the zero to 60 contest, a 408 is way overkill; IMO you can put a 2bbl on it and still spin, maybe to 60mph.
              In the zero to 60 contest, the 340/4-speeds were killer combos; just about 300horsepower. They just needed better tires than those stinking E70-14s :(
              You can pump up a 318 to that, and she won't boil the hides so bad. Put 4.30s on a smogger-teen and watch her come alive.

              What I'm saying is you already have 165 more horspower than you need and probably 200/250 more than the chassis can handle, so I understand your desire to make the 408 the best that she can be, but honestly, in the street contest, with street suspension, without intending to sound like a prick; what's the point? You can disconnect the secondaries and at least one cylinder, and still waste/ nearly waste, most street non-strokers.
               
              Last edited: Feb 20, 2021
            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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              Like and agree
               
            • chinze57

              chinze57 Push Button tranny and a Slant 6 that'll never die

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              That’s what it’s about for me. Sure, I’d like to not have to do floor mods, but if I need to for the result I want to fit with what I’ve got, I’ll do it.
               
            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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              Thanks guys , as always; just trying to help.
               
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              • AJ/FormS

                AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                IMO
                a 4-speed automatic with a hi-stall and loc-up. is a better idea than a GVod behind a Mopar automatic.
                Yur 4-speed auto will act like a 5.5 speed.
                You wanna see how?
                Ok I'll give you the short version;
                The Hi-stall will give you an extra bottom gear, and the loc-up will give you a half a gear for cruising, so 4 +1 +.5=5.5
                But IMO, the A500 has ratios that are way too far apart, and the A518 are still too far apart.
                All the gears are in the same case, so you don't have to deal with the add-on GVod. And you can never bust the GVod by backing up with it still engaged..... Like I did. If I was not a stick-man, I would open up the tunnel in a heart beat.
                The A500 has a starter of 2.74 and finishes at .69 for a range of 2.74/.69=3.97, which,IMO, is too broad, and individually, the gears are a lil too far apart for performance, for a small block, but not for a stroker.
                The A518 is 2.45/.69=3.55 still too far apart for a 4 speed. But the Chevy's are not much better, most are actually worse. But they are more compact and fit better in the tunnel with less mods.

                Page 2
                Suppose you were geared for 65=2200, which will take 3.91s with a .69od.
                Lets look at what the math says; your road gears are (trans times diff)
                9.58-5.67-3.91-2.70 But is that what your engine sees?
                no
                the convertor is in between them, adding it's ratio that varies continuously with torque input and roadspeed. At zero mph the ratio may be as high as 1.8 and at 100mph it might be as low as 1.1.. Thru each gear the ratio will vary with torque input so we will have to average the TM(Torque Multiplication) by guesswork.
                Let's use
                1.6 on the start line; then
                1.4 thru the rest of first, then
                1.3 in second gear and
                1.2 in third. then
                1.1 in overdrive, then
                1.0 in od/locked up.
                So your new ratios are ;
                say average of 15.33/13.41-7.37-4.69-3.24-2.70
                Count them; I see 6, but lock up is only worth 200 to 250 or so.
                So I call it a 5.5
                as to splits I see;
                .87-.55-.64-.69-.83
                So lets say you have a shift-rpm of 5500. Then on each shift, your rpm will fall to those percents. On the 1-2 to 3025, on the 2-3 to 3520,on the 3-4 to 3795, and into locup at 65 , from 2425 to 2200, or 225rpm in this case.
                Of course this assumes a stall of 3025 or less.
                So now
                Because the 5500 shift dictates a power peak of about 5200, your powerband has to be from 3025 to 5200=2175; that's pretty big , but you can get away with smaller on the 1-2 so going by the third gear, the powerband could be as small as 5200 less 3520=1680; there yago.

                But just to remind you; 5500 at the top of 1.45-second gear with 3.91s is 64 mph, so as a streeter, what do the numbers really mean?
                Answer; IMO, not much. Go ahead, determine your zero to 60 times with any two rear gears you want. If the tires spin all thru first, I doubt the results will be meaningful. If you have to peddle it to get traction, yurdone.

                But that does not negate cruising at 2200 in .69od versus 3200 both with 3.91s. And even if 3.91 are not quicker to 65 in real time; it will certainly feel quicker. Fix the tirespin and then it will be quicker.
                My 2cents
                Now you just gotta figure out how to satisfy her need for cruise-timing at 2200 rpm.
                 
                Last edited: Feb 20, 2021
              • RustyRatRod

                RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                And you do a great job. I just like pokin the stick every now and then. lol
                 
              • RogerCox

                RogerCox Well-Known Member

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                yeah knowing what I know now I would have gone with a different trans instead of trying to keep it mopar. But I’m stuck with the 727 3 speed auto now.
                 
              • chinze57

                chinze57 Push Button tranny and a Slant 6 that'll never die

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                That’s what it’s about for me. Sure, I’d like to not have to do floornmods
                If I didn’t have the Pushbutton automatic, I would absolutely go for a different trans. I just think it’s too cool of a feature to get rid of.
                 
              • toolmanmike

                toolmanmike Moderator Staff Member FABO Gold Member

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                Depending on your combo you might have a lot to play with. If you have a stroker, they have a lot of torque and don't need a 3.73 or 3.91+ to make it work. With a modest gear (like a 3.23) and a lot of torque, you can burn tires at will and still cruise at 65 on the highway at around 2500 rom or so. Like the best of both worlds without a overdrive.
                 
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                • jos51700

                  jos51700 Green Bearing thread connoisseur

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                  Personally, I never liked the gear vendor unit hanging off the back of the trans like that. I see that they have a shorty model now, but if imma do that, I might as well run a 518 and be done.

                  That said, how's come I can't split gears with the OD unit on a 518? I don't want to, but I'm not a transmission guy and I'm just curious.
                   
                • AJ/FormS

                  AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                  On the electric shifts you could, but that .69 is brutal, the shifts are better thru the main box. The A518 ratios are
                  2.45-1.45-1.00-.69od with splits od
                  .59-.69-.69
                  splitting gears you would get.
                  2.45-1.69-1.45-1.00-1.00-.69 split gears in red.

                  and I have no idea how much power you could jam thru that planetary overdrive
                   
                • Jesus Chrysler

                  Jesus Chrysler Forgiving Sins Against Mopar Since 1983

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                  I agree about the hot rodding and cutting, but I also understand why many feel some cars just shouldn’t be cut up. I would like to run a GV in my barracuda if I can get away with not having to slice up the tunnel. I could live with a few hammer dings though. Then again, if I pull my carpet up and start poking holes through rust, maybe I’ll consider a 5 speed. It seems pretty solid from underneath, but that’s just from my minimal time spent groveling under there during a fuel line swap.

                  oh, and that 2000 year old story ain’t no passing fad!
                   
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