3.08 vs 3.23 with Muncie m20

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

  1. 436'd Skylark

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

    I'd stick with the muncie if you already have it.
     
  2. philbquick

    philbquick Founders Club Member

    Yes, it's not good to bog an engine, it's good to hit the sweet spot.

    Sounds like your a little under 300 hp. If you're planning to bang gears constantly and drag race it may not hold up. If you drive it sensibly you'll be ok. They put 300+ through the old Saginaw peanut transmissions in the early Corvettes and they did ok.
     
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  3. BrianTrick

    BrianTrick Brian Trick

    You already have the Muncie setup in there and working,so I would leave that alone. You are a gear change away from having it right. A 3:23 or 3:42 would be a good fit for that. If you had a close-ratio M21,I would definitely go for the 3:42.
     
  4. 87GN_70GS

    87GN_70GS Well-Known Member

    I had an M21 with 3.23, an absolute dog in first gear (7.1 overall gearing in first). I prob needed 3.42 or 3.55 (7.5 to 7.8 overall). I would recommend 8:1 minimum overall in first which means with your 2.52 first you need 3.23 or better
     
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  5. JoRion

    JoRion Member


    A fair point. Interesting that some people say these transmissions hold up behind a big block. Others say plan on breaking them.

    That m21 with a 3.23 rear is pretty close to what I have now. So you know what I'm dealing with. A 3.23 would be an upgrade forsure. And maybe the best compromise for around town and highway driving.
     
  6. knucklebusted

    knucklebusted Well-Known Member

    I have a 71 GS 350 4-speed and it came with an M21 and 3.08 gears. It sucked off the line. It was so close that I often went 1st to 3rd because 2nd didn't change much. I've since swapped an M20 into it and it is a lot better but I'm now looking for the M23Z gear set that has a 2.98:1 first gear. It would turn your 2.73 gears into the equivalent of 3.28:1 rear gears with a very nice cruising RPM. The trouble is those gears are hard to find right now. Nobody has stock.
     
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  7. 87GN_70GS

    87GN_70GS Well-Known Member

    That (M23Z) is what I have currently, bought it a couple years ago. With my current 3.31 rear, I have 9.86:1 in first. Should be perfect
     
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  8. Dano

    Dano Platinum Level Contributor

    I had a stock '70 w/3.23 & M-21 if that's m/l your starting pt. w/M20 & 2.73 - It wasn't bad. Maybe the higher HP '70 350 engine helped. Not that you're planning to race it, but the change to 3.42 was worth a couple tenths & then 3.73 a few tenths more. Being that you're dealing w/an 8.5, I'd even consider 3.55's. I drove mine w/3.73's to the Nationals (700 mi. ea. way) and it wasn't bad.
     
  9. JoRion

    JoRion Member

    That would be the ideal solution.

    I took the car out this eve. First time really testing on it, after putting in a TA Performance HEI. Once the car is moving, she is a blast to drive. But the acceleration from a stop is horrible. Definitely will start looking at putting in a 3.23 – maybe the 3.42. It will be way better on the clutch, that's for sure.
     
    Dano likes this.

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