Will a stock 8 1/4" SG with 3:55's hold up??

Transmission and Drivetrain Tech

  1. Veryfastdart

    Veryfastdart Well-Known Member

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    I have a 416 stroker going in my 71 scamp.
    Approx HP 475, maybe more. Having it dyno'ed this winter.
    My question is will a stock 8 1/4" rear hold up being street driven and occasional track raced with street tires?
    THX
     
  2. RustyRatRod

    RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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    Probably so. If you put slicks on it and really try to get it to hook, you may find its limits. But with good axles and a good sure grip unit, it will take some abuse. Even with slicks.
     
    • Agree Agree x 4
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

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      Yes it will. Now a lot depends on how much abuse your handing out. Torque level, not so much HP, RPM launch, car weight, how much grip there is. This all of course puts stress on the gears.

      Numerically higher gears are of course more torque release. More stress.

      The 8-1/4 is underated but will take only so much abuse in a heavy high rpm launching car.

      I wouldn’t worry if you did 1, 2 or 3 days a year drag racing and the rest street driving since street tires give in easy.

      IMO, you’ll be fine.
       
    • Veryfastdart

      Veryfastdart Well-Known Member

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      Excellent
      Thanks you very gentleman.
      This site is full of very knowledgeable, helpful and friendly people.
      I have an 8 3/4" that I am setting up for the car, but It is not ready and I have an 8 1/4" SG that's ready to go in so I can still drive the car.
       
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

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      Oh nice! You’ll be hard pressed to damage the 8-3/4 at your power level.
      Are you upgrading the axles?
       
    • Veryfastdart

      Veryfastdart Well-Known Member

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      Yes, I was thinking of Dr Diff 30 splines with green bearings?
      I am installing their rear disc kit and going from SBP to LBP.
      Any comments or suggestions?
      I also haven't picked a final gear yet. I have 3:23 pumpkins but a lot of A bodies run 3:91's?
      I'm thinking 3:55's? I guess I will see how I like them with the 8 1/4" first??
      I am going with the widest 15" tire without mini tubbing yet??
      Probably a 255/70/15 or 255/60/15
       
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

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      In my 8-3/4, I went also went with Doc Diff’s axles as well but stayed with the stock bearings and such.

      As far as your gear ratio is concerned, much depends on wht your focused on mostly and what your willing to live with. Lower numerical gear ratio 3.23, 2.94, etc.. will require more stall, smaller tires to get moving, etc...

      Higher numerical gears will require less stall and you can use larger tires.

      Visit the tire and rim thread of what fits and what other people have done. Those tires will fit.
       
    • OL DODGE

      OL DODGE Well-Known Member

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      I had a stock 73 Charger SE with a 400 2 bbl big block ,727, and was tooling along 20mph when the 8 1/4 decided to lock up-it left longer marks in my underwear than the locked up tires did to the pavement. Culprit was a cracked gear tooth wedged in the ring gear. I myself would just be patient and wait-after my experience, I would rather overbuild . Just my experience. I never raced that car(street or otherwise-btw)
       
    • Veryfastdart

      Veryfastdart Well-Known Member

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      Rumblefish, I have ATI build my converters. I sure you are very familiar with what is needed for a custom converter. They base it on HP/TQ, cam specs, weight of vehicle, tire size and gear ratio. 4 out of 5 I don't have yet! lol Thanks for the info. Just curious, why stock tapered not greens? Side load?
       
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

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    • Veryfastdart

      Veryfastdart Well-Known Member

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      Great
      I agree, there is NOTHING wrong with stock bearings, but it is nice not to have to adjust that dang pre load setting contraption!
      Thanks for the tip on the converters, I'll give them a look.
       
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

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      Ehhhh, no problem, the whole rear was set it forget it. Once everything is set up from end to end and inside, it’s nothing. My 10 YO son can do this. I also didn’t do anything weird like narrow the housing or start in with aftermarket brake systems or drum to disc. Not that doing such makes it any more difficult. It’s just the K.I.S.S. method so it is just all the same chit we been messing with since we’re kids, so there’s no surprises.

      (LMAO! I have more problems remembering this crap than anything else.)

      Those converter guys have been down the block from me for many years and are widely known locally.

      I also worked with the local transmission legend, high performance, 4r70w, transmission, AOD, racing, Freddy Brown
      He also does some interesting work.
      A friend of mine went to him and they put a Ford AOD behind his small block Mopar. Weird right?
       
    • Veryfastdart

      Veryfastdart Well-Known Member

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      Sweet
      Thanks
      I am putting disc brakes on the rear
       
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