Register now to get rid of these ads!

Technical Rear end ratio advice

Discussion in 'The Hokey Ass Message Board' started by belair, Nov 4, 2017.

  1. belair
    Joined: Jul 10, 2006
    Posts: 8,717

    belair
    Member

    Got the 58 Apache close to road ready. Running a 350 and a 2004r, B&M kit to shift off of pressure. Looks like I have a 2:73 rearend from a 73 firebird, if I remember orrectly. What would be a range of acceptable gears to replace the 2:73s? Will be running 235 or 255/15s. I'm thinking 3:42 or maybe a 3:73 ( TA or Z/28?). What would be good cars for a swap-I could do an entire rear end by myself, have never done a ring and pinion. Thanks.
     
  2. woodbutcher
    Joined: Apr 25, 2012
    Posts: 3,254

    woodbutcher
    Member

    :D Just gonna take a big ole WAG here.Maybe some where in the neighbor hood of 3.55`s,or a bit lower.
    Good luck.Have fun.Be safe.
    Leo
     
  3. weemark
    Joined: Sep 1, 2002
    Posts: 819

    weemark
    Member
    from scotland

    I would probably go with something like 3.90s for the 200r4.
     
  4. You'd be happy with 3.70'ish rear end ratio, given your tire and transmission combo...........have a 200R4 behind 383 stroker in my 65 Impala wagon with stock 3:36 rear gear, run 245/15's on back, and this combo doesn't like O/D until at least 60 mph........will change ratio to 3:70's soon..........
     
    pprather likes this.

  5. fiftyv8
    Joined: Mar 11, 2007
    Posts: 5,202

    fiftyv8
    Member
    from CO & WA

    3.70:1 or higher numbers for serious hauling but just for street running around empty and the odd small chores 3.54:1 is very suitable
     
  6. Gman0046
    Joined: Jul 24, 2005
    Posts: 6,260

    Gman0046
    Member

    3:73 would be my choice.
     
    Last edited: Nov 4, 2017
    APACHE FS and caseywheels like this.
  7. Sheep Dip
    Joined: Dec 29, 2010
    Posts: 1,572

    Sheep Dip
    Member
    from Central Ca

    A 3.90 rear ratio would give you roughly a 2.93 od ratio. The 200r4 has a 0.67 od.
    Keep in mind that the 200r4 burns about 70 hp just to operate it vs 35 hp for a Turbo 350
     
  8. squirrel
    Joined: Sep 23, 2004
    Posts: 49,338

    squirrel
    Member

    transmission don't "burn hp" "just to operate". They take a percentage.

    otherwise, cars wouldn't creep in drive, at idle, would they?
     
    firstinsteele likes this.
  9. Deuces
    Joined: Nov 3, 2009
    Posts: 20,598

    Deuces
    Member
    from Michigan

    The 3:42 or 3:55 gear set is all you need for around town cruising.... In my opinion anyway....:rolleyes:
     
  10. Sheep Dip
    Joined: Dec 29, 2010
    Posts: 1,572

    Sheep Dip
    Member
    from Central Ca

    Well excuse me for not using the "Proper Terminology", but I think everyone gets the picture that HP is robbed through the whole drive train operation at different power applications with the automatic trans component's being the biggest drain.
     
    H380 likes this.
  11. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,283

    Kerrynzl
    Member

    Leave the gears as-is.
    But change the cam to a short duration retro-hydraulic roller [200 deg duration] and put a small carb on it ,so it purrs like a kitten

    With 25-1/2" diameter tyres it will cruise at 1600rpm at 65mph [similar to a modern car] and get decent mpg's.
    You'll be able to use your pickup as a long distance cruiser without pounding your eardrums. Around town the low end torque and lower 3 gears come into play.
     
  12. squirrel
    Joined: Sep 23, 2004
    Posts: 49,338

    squirrel
    Member

    There are lots of ways to skin this cat. 3.42 to 3.73 gears would work well. You could also try it with the gears you have in it now, you may like it just fine, Or not, hard to say.
     
    APACHE FS likes this.
  13. fordflambe
    Joined: Apr 9, 2007
    Posts: 554

    fordflambe
    Member

    Rear gears in cars are like Hooters on women.............the bigger the better!
     
    Blues4U likes this.
  14. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,283

    Kerrynzl
    Member

    Don't you mean the newer the better.:p
    A set of 1999 manufactured gears [18 years] is made of a lot higher density "metallurgy" than 1947 gears [70 years]
     
    blowby likes this.
  15. fordflambe
    Joined: Apr 9, 2007
    Posts: 554

    fordflambe
    Member

    Knowing a little about my pals, maybe I should have made the statement "fill in the blank"...................
     
  16. Budget36
    Joined: Nov 29, 2014
    Posts: 6,788

    Budget36
    Member

    Suggest you just run what you have, then determine what you might want. My kids car (OT) has a 2.77 rear, stock 350 with a 700R4, weighs a solid 3800lbs as I recall...no issue in town, or on the highway.

    Now if we put in a bigger cam, stall converter, higher breathing intake and induction, we might re-think what's in there...but she just cruises it....but then again, why are her rear tires wearing out faster than the fronts?
    And she pulls early 20's MPG on freeway driving.
     
  17. i think it depends on what you want to do with the truck. big cam, pulling loads or hot rodding around town? i would go lower gears. stock motor ,flat terrain and long trips leave those gears and see how "bad" they are.
     
    slowmotion likes this.
  18. belair
    Joined: Jul 10, 2006
    Posts: 8,717

    belair
    Member

    It's just going to be a driver. Stock cam, aluminum intake, Q-Jet, headers. I have driven it around, feels pretty gutless at take-off. And I don't want it lugging in OD at 65-75.
     
  19. squirrel
    Joined: Sep 23, 2004
    Posts: 49,338

    squirrel
    Member

    Does it have a tach? If so, that might make it easier to figure out what you want.
     
    firstinsteele and belair like this.
  20. Bigdavid
    Joined: Feb 10, 2012
    Posts: 37

    Bigdavid
    Member
    from Tennessee

    With the 273 gear you’ll run about 1600 rpm in overdrive at 70 mph
    With the gear ratios in that 200r4 it shouldn’t lug anywhere
     
  21. belair
    Joined: Jul 10, 2006
    Posts: 8,717

    belair
    Member

    Gonna put a tach in it Monday, Jim. Good info, Bigdavid. Thanks.
     
  22. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,283

    Kerrynzl
    Member

    What's the tyre diameter?
    If you're got 25-1/2" Tyres , try a 3.36 ratio and at 65mph it'll be cruising at 2000 rpm [75mph= 2300rpm]
    The 200R4 has a lower 1st than a T350
    A 3.36 ratio with a 200R4 is the same in 1st as a T350 with a 3.65 ratio in 1st.
     
    belair and Bigdavid like this.
  23. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 8,841

    mgtstumpy
    Member

    At highway speed (60-65mph) you want your rpm to be between 1800rpm and 2100rpm. My 35 Chebby with 3.54:1 and 235:75 tyres is 1,879rpm at 65mph. My OT DD with 3.73:1 and 235:75s is 2,121rpm. 2.73:1 is IMHO too high for an OD transmission, engine will labour in OD.

    At 65mph a 200R with 235:75 tyres, engine speed is:-
    • 1,387rpm with 2.73:1;
    • 1,707rpm with 3.36:1;
    • 1,799rpm with 3.54:1; and
    • 1,895rpm with 3.73:1.
    So many options and as Jim stated, there are many ways to skin a cat.
     
    pitman, belair and gimpyshotrods like this.
  24. dan31
    Joined: Jul 3, 2011
    Posts: 1,081

    dan31
    Member

    Check out Wallace racing rear gear calculator. Your stall speed and type [lockup or non] may come into play .I would think that 3.73's would be close.
     
    belair likes this.
  25. 52HardTop
    Joined: Jun 21, 2007
    Posts: 954

    52HardTop
    Member

    My 51 convertible is running a crate 350 with 373s in a 10 bolt Nova rear. It is quick enough from the traffic lights and cruises 65 to 70 nicely. If it's a cruiser you want, the 373s were always the gears that I've seen recommended. I'm even using the same gear in the rear of my 52 Hard Top with a 235 and T-5 combo.
     
  26. belair
    Joined: Jul 10, 2006
    Posts: 8,717

    belair
    Member

    Thanks for the hard numbers and real world info guys. This is what Im looking for. And a 78-81 Z28 rear end ;).
     
  27. southcross2631
    Joined: Jan 20, 2013
    Posts: 4,414

    southcross2631
    Member

    Most of the last of the rear wheel drive Chevy police cars had 235/70r15 tires with a 700 overdrive and ran 3.42 gears. Not all ,but most some had 2.73 some had 3.08.
     
  28. 3.73's!
     
    belair likes this.
  29. slowmotion
    Joined: Nov 21, 2011
    Posts: 3,276

    slowmotion
    Member

    3.55-3.73s should work out pretty well from the info and intentions you've mentioned. Nothin' worse than having a pig that can't get out of it's own way on the low end. Still should cruise decently at highway speeds w/ the OD trans and a set of fairly tall tires.
     
    belair likes this.
  30. Black Panther
    Joined: Jan 6, 2010
    Posts: 1,767

    Black Panther
    Member
    from SoCal

    One thing to keep in mind is that the late model cars that ran these OD transmissions and gears on the taller side is that they were fuel injected and had computer controls. If you're running a carb, you'd have to be about 1800-1900 rpm on the low side or your car will be pretty unresponsive/bogging at freeway speeds and your fuel mileage will suffer. Obviously lighter cars can tolerate taller gears in this situation...but right about 1900-2100 highway cruising rpm is pretty ideal I think..
     
    belair likes this.

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.