How much gain with lower gears?

Mopar Performance Issues

  1. 19blockhead72

    19blockhead72 Well-Known Member

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    So just to keep it simple I'm running a mild 408 in my Sport. It's 90% a street car that will see some weekend bracket racing. I'm currently running 323's in a 8.75 suregrip that's perfect for the street. The center is older and I was planing a rebuild soon. If I went to a 3.55 or at the lowest 3.73, how much could I possibly shave of my et.? I have not run the car on the track yet, just wondering if it would be a dramatic gain or if It would just be a tenth or two. Thanks
     
  2. brian6pac

    brian6pac Well-Known Member

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    I would calculate how fast the car will go at a certain RPM, say 6000 that is all the faster you want to spin it and say you want your top speed to be 130 MPH and you have 28" tires = 3.73:1 that would be 134 MPH
     
  3. Darter6

    Darter6 Well-Known Member

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    You will see several tenths shaved(as much as 4 tenths possible) if you choose the 3.73's over the 3.23. A 408 will like them.They are quite street friendly and not too bad on the open road with speeds under 65.Several of my PA friends run them in their street cars.They are from south western part of the state with lots of hills and twist and turn roads.Not many places to top out the speedo so tighter gears work well in that area.Gettysburg is a bit hilly if I remember.Not as flat as the south eastern part of the state. Out here I have open long stretches of flat land. 2.76 feel like 4.10's with no overdrive.
     
  4. 19blockhead72

    19blockhead72 Well-Known Member

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    Many years ago I ran 3.91's in Plymouth and 4.10's in a hot rod I had. Certainly wouldn't want to road trip any long distance with them but If I could gain more than a couple tenths I may install something lower. I just keep thinking about that possible long road trip I might do with it and dread that low gear. Of coarse someone will soon mention an overdrive transmission but I really just want to stick with my simple "old school" setup.
     
  5. brian6pac

    brian6pac Well-Known Member

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    there are many calculators online check some out 3.73 28" 59mph = 2650 rpm
    no problem with that!
     
  6. 19blockhead72

    19blockhead72 Well-Known Member

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    Yeah, good call. I'll though some numbers at one and see what I get. I was more courious how much I could gain in a quarter mile et by going from a 3.23 gear to say a 3.73.
     
  7. mopowers

    mopowers Well-Known Member

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    What size tires?
     
  8. replicaracer43

    replicaracer43 Old school member

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    Your won't know till you run a back to back test, but odds are, you won't see much difference going from 3:23 to 3:73 with your 408.... I have ran a 3:55 gear, swapped in a 5:13 and the car ran the EXACTLY same et
     
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    • 19blockhead72

      19blockhead72 Well-Known Member

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      That's what I was wondering. Maybe I'll just leave them in and see what I get. I was going to freshen up the center next week and thought while I had it apart it would be easy to swap gears if there were gains to be made. I guess it's a more trial and error thing than an exact science.
       
    • famous bob

      famous bob mopar misfit FABO Gold Member

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      this sounds a little weired. maybe a bigger traction problem w/ lower gears ? car not set up right?
       
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      • 19blockhead72

        19blockhead72 Well-Known Member

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        25.5 tall
         
      • mopowers

        mopowers Well-Known Member

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        That's a pretty short tire. I'd be willing to bet you won't pick up any ET in the 1/4 going from your 3.23s to a 3.55 or 3.73 with your mild 408. With my old 408 duster, i ran identical ETs with 3.23, 3.91s and 4.88s. I was a kid then and had no clue what I was doing, but they're data points none-the-less.
         
      • replicaracer43

        replicaracer43 Old school member

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        Nope, car was on slicks, was dead consistent, the gear swap was a experiment to see what the car would do...it was crazy, it ran EXACTLY the same ET as I'd did with the street gear
         
      • RustyRatRod

        RustyRatRod Weenie idiot loser. FABO Gold Member

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        Maybe 1/2 second with the 3.73.
         
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        • mopowers

          mopowers Well-Known Member

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          Has the current combo been run yet?
           
        • 19blockhead72

          19blockhead72 Well-Known Member

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          No, it will be a few weeks till I get it to the track. I'm excited to see what it's got but afraid I may be disappointed. If it's slower than a 13.2 I may cry.
           
        • moper

          moper FABO Gold Member FABO Gold Member

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          Without knowing what it's doing now, it's impossible to guess. It's easy to put too much gear into a street car package and lead to more issues. My advice would be get some track time and work out the bugs. If you can get it consistent, try rasing the shift points by a few hundred rpm each run. If it goes faster more gear should help. If it doesn't don't bother.
           
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          • famous bob

            famous bob mopar misfit FABO Gold Member

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            if all is right suspension wise, I AGREE W/ THIS , --DONE IT !
             
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            • 273

              273 Well-Known Member

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              1st thing I do is take it to the track and dial it in as is. Then go from there. Easier to figure out from a starting point. Cause you will know your mph, peeps can figure out how much potential you have with your ET and figure out your optimal gear then decide if you want that or something in between or stick with what you got.

              I got to do the same thing with my 2.96 geared magnum engine.

              Plus the main benefit with 408 is you can run less gear than a 360. You running 3.23 is like a 360 running 3.73 and you running 3.73 is like a 360 running 4.30 etc..
               
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              • B3422w5

                B3422w5 Well-Known Member

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                As others have said, you wont know anything till you get to the track. If your bracket racing your looking for consistency first.
                If your happy with what it runs and its repeatibility, leave it alone.
                Change gears, it likely will ET better, how much is guessing at this point.
                Remember though, should you change to a steeper gear, you open the possibility of possible traction issues and perhaps tuning changes.
                That why street strip cars usually give up something to do one or the other in excellent fashion. Rarely are they great both ways. Just have to figure out whats most important to you
                 
              • 19blockhead72

                19blockhead72 Well-Known Member

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                More less this question came about because I was planning on rebuilding the rear before going to the track just to sure it up. I just figured while I was in there I might change the ratio too. Anyway I found 3.73 gears and thought they would be a nice compromise. Love them so far but still haven't gotten to the track yet.
                 
              • forphorty

                forphorty Well-Known Member

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                What converter?
                 
              • ir3333

                ir3333 Well-Known Member

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                camshaft numbers?
                 
              • SpeedThrills

                SpeedThrills Well-Known Member

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                These questions come up frequently because the way to make a car faster is:
                1) Buy speed part.
                2) Install, test.
                3) Remove speed part after disappointing test.
                4) Put part on shelf.
                5) Repeat until success is achieved.
                 
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                • B3422w5

                  B3422w5 Well-Known Member

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                  Based on the lack of info given, its impossible to say. Convertor, cam, carb, compression, etc.
                  Its extremely unlikely you will see enough difference to like the change.
                  Those saying 1/2 a second..... haha. Cant see any way just a gear change by itself willl make that kind of change.
                  I have never seen even a tenth, ever, on any gear swap i have ever made.
                   
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