Register now to get rid of these ads!

Technical 331 Hemi RPM question

Discussion in 'Traditional Hot Rods' started by sdimpala64, Nov 29, 2018.

  1. sdimpala64
    Joined: Mar 5, 2009
    Posts: 49

    sdimpala64
    Member
    from SD CA

    Trying to decide what gear to run behind a stock 331 Chrysler Hemi in a Model A with automatic transmission.
    Tire height will be 31.5 inches, Calculations at 75 mph:
    Gear RPM
    2.75 2259
    3.00 2464
    3.25 2670
    3.5 2875
    Will spend a good amount of time on the highway.
    Any recommendations are greatly appreciated. Thanks.
     
    Last edited: Nov 29, 2018
    loudbang and Bandit Billy like this.
  2. Some info on the engine specs would be helpful, but if highway running was my main concern, I would be going for the 2.75 gear set. A properly built 331 will have plenty of torque down low to get a light weight Model A moving with that tall of a rear gear.
     
    loudbang likes this.
  3. My 32 has 3.48s with 31.5s and no overdrive. Different engine, but still a small V8. I like the combo. Its not too buzzy while giving enough gear to move well with only 300 (if that!!) or so HP.
     
    loudbang likes this.
  4. town sedan
    Joined: Aug 18, 2011
    Posts: 1,290

    town sedan
    ALLIANCE MEMBER

    Slush box, or stick shift? It will make a difference in how the car drives. I'd stay in the 3.25:1 to the 3.50:1 range with a stick shift.
    -Dave
     
    Register now to get rid of these ads!

  5. sdimpala64
    Joined: Mar 5, 2009
    Posts: 49

    sdimpala64
    Member
    from SD CA

    FrozenMerc: Completely stock rebuild is what I was told.
    town sedan: automatic transmission(no overdrive)
     
    loudbang and town sedan like this.
  6. foolthrottle
    Joined: Oct 14, 2005
    Posts: 1,033

    foolthrottle
    Member

    the higher ratio worked for me for long distance 75 plus speeds something like 3000 RPM the early hemis don't like the higher revs. mine was a 331 hemi 750 cfm carb, GM ignition, th400, GM 12 bolt posi 2:90 with that set up I could buzz up over 120 without going over 4500 RPM
     
    loudbang and town sedan like this.
  7. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 6,332

    Bandit Billy
    ALLIANCE MEMBER

    I am building a 330 Hemi for my truck. I already had built the 9 inch posi with 3:70 gears. In-between is a A518 overdrive automatic. If I was not running an OD I would not have exceeded 3:55. If it helps.
     
    loudbang and 73RR like this.
  8. DOCTOR SATAN
    Joined: Mar 21, 2014
    Posts: 711

    DOCTOR SATAN
    Member
    from okc

    Quickie solves all your worries, holler if ya need one.

     
  9. 73RR
    Joined: Jan 29, 2007
    Posts: 6,290

    73RR
    Member

    For extended highway use I'd keep the rpm below 3000, not beause the engine won't tolerate more, but just because of the inherent noise generated.

    .
     
    loudbang likes this.
  10. foolthrottle
    Joined: Oct 14, 2005
    Posts: 1,033

    foolthrottle
    Member

    this is the engine running in neutral
     
    Rick28 likes this.
  11. sdimpala64
    Joined: Mar 5, 2009
    Posts: 49

    sdimpala64
    Member
    from SD CA

    Thanks to all who responded.
     
  12. Brand Apart
    Joined: Jan 22, 2011
    Posts: 604

    Brand Apart
    Member
    from Roswell GA

    I agree with 73RR. (Pretty much always)
    Side note. I'm doing a 354 and hoping to be cursing at 75 at approx 2300, but am quite a bit away from testing it out.
     
  13. sdimpala64
    Joined: Mar 5, 2009
    Posts: 49

    sdimpala64
    Member
    from SD CA

    After talking with 73RR I have chosen to go with 3.25 gears. Thanks again
    to all the members that responded.
     
  14. George
    Joined: Jan 1, 2005
    Posts: 7,192

    George
    Member

    OEM with the OEM 2 speed tranny was 3.36.
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2020 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.