3.08 vs 3.23 with Muncie m20

Discussion in 'Got gears?' started by JoRion, Oct 26, 2020.

  1. JoRion

    JoRion Member

    Hey all,

    Just finished swapping a Muncie M20 into my 72 skyark 350 2bbl. Relatively stock engine – may have had a cam upgrade before I got it, but still a very mild build.

    I had read that the stock 2.73 gear would not work well with the m20. I figured I would give it a try and change out the gear and pinion if need be. Well. It is a dog. Very slow from a stop. Hill starts really bog down the engine. It just isn't fun unless the car is moving.

    So, the question is, what is the better fit? the 3.08 or the 3.23. I live in a city, so there is lots of stop and go traffic. But would like to take the car on longer treks out of the city. So, all around driving – including highway driving would be ideal. That being said, I can't have the car bog down in everyday traffic. She needs to be a good all around driver.

    Second question. Is it pretty straightforward changing out the gears? I had already changed the axle seals and bearings earlier when I was still driving with the th350. Not looking forward to pulling the axles again.
     
  2. telriv

    telriv Founders Club Member

    3.08 or 3.23
     
  3. Bens99gtp

    Bens99gtp Well-Known Member

    I would go 3.23 personally

    And if unbolting 4 bolts per axle is taxing to you, I wouldn't recommend doing the gear swap. Bits nit physical hard, but they are tedious....a few thousandths is enough to screw it uo and it eat itself
     
    Dano likes this.
  4. JoRion

    JoRion Member

    I didn't mean it was taxing. I am just trying to get a more detailed view.

    And see what everyone's experiences are with the two gear sets.
     
  5. BrianTrick

    BrianTrick Brian Trick

    If you have a 2:73 now,you will not notice much of a difference moving up to a 3:08,but you will notice an improvement jumping up to a 3:23.
     
  6. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I'd run 3.42s. Great all around gear and good on the highway.
     
    Dano likes this.
  7. Bens99gtp

    Bens99gtp Well-Known Member

    Being a 72, you should have and 8.5. If changing gears to any ratio......nows the time to add posi if you don't have it....
    What size tires are you running now??

    On a 27" tire 3.42 gears will get you pushing 2800 rpms at 65mph. Where 3.23 would be more in the 2600 rpm area at 65mph
     
  8. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    And despite popular belief you can spin your engine 3k plus all day without hurting a thing..
     
  9. philbquick

    philbquick Founders Club Member

    I'd go 3.23. Changing gears is a process, pinion depth, pinion preload, carrier preload and back lash must all be set. Some special tooling is involved for pinion depth, preload can be done with a 1/4" flex beam torque wrench and you should probably have a press to change the bearings. When you go from "2" series to "3" series ratios I'm pretty sure the entire carrier must be changed. We have an axle shop in this county that specializes in this stuff. Really, a Saginaw 4 speed transmission with a 3.11 first gear would probably do what you want with a 2.73 rear and 4th gear would almost be like overdrive.
     
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    72 Skylark should be the 8.5 10 bolt, stock gears for the 350-2bbl were 2.56. Carrier breaks are 2.56 and down, and 2.73 and up. So, yes, you need a different carrier.
     
  11. JoRion

    JoRion Member

    Thanks for the input.

    The car definitely has an 8.5 10 bolt 2.73 – not 2.56.

    I hadn't thought about going over a 3.23. You all gave me somethings to think about.

    I had thought about putting in a saginaw originally, but was talked into going with a muncie, and found one for cheap.
     
  12. Bens99gtp

    Bens99gtp Well-Known Member


    This is very true.....most its not the engine wear that most ppl worry about.....I would think most ppl when they are dealing with highway speeds are wanting to get some mpg too......so its a balancing act for sure....

    I see boat motors go 4000+hrs that gave lived above 3000 roms for most of that time
     
  13. JoRion

    JoRion Member

    That is definitely playing into the decision making.
     
  14. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I got 15 mpg with my 430 with an m20 and 3.42s going 75+ on the highway on many 8 hour or longer trips. I was happy with that.
     
    JoRion and Quick Buick like this.
  15. BrianTrick

    BrianTrick Brian Trick

    You can also get poor mileage by not having enough gear.
     
  16. Bens99gtp

    Bens99gtp Well-Known Member

    Can't complain about that at all. Real world proof
     
    JoRion likes this.
  17. Bens99gtp

    Bens99gtp Well-Known Member

    This too is equally as true.......the balancing act
     
  18. Dano

    Dano Platinum Level Contributor

    3.23 or preferably 3.42. You won't be sorry w/3.42's & on the highway it'll be fine up to any reasonable (70-80 mph) speed esp. w/a 350.
     
    Starc Traxler likes this.
  19. JoRion

    JoRion Member

    Funny how this works. Came here thinking 3.08 or 3.23, now I'm thinking 3.42.

    Since a Saginaw 3.11 was brought up here. How would that hold up? I have read mixed opinions on the transmission – some say it will do fine, some say it wont hold up. Since this is a relatively stock 72. The hp and torque ratings on the engine are pretty low. And I wont be power shifting or doing any clutch dumps. Is that a viable option?
     
  20. telriv

    telriv Founders Club Member

    Yes Now you don't need to change rear gears.
     

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