Gearing options

Discussion in '7.3L PowerStroke Power & Performance' started by Kurt, Jun 19, 2021.

  1. Kurt

    Kurt SDD Junior Member

    Messages:
    1
    Likes Received:
    0
    Joined:
    Jul 30, 2019
    Location:
    Michigan
    Looking for some experience or opinions for gearing options. The truck is a 99 350 with the zf6 trans 4x4. Originally the truck had a 10" lift with 40s and 4.56 gears. Since then I have dropped to and 8" lift and currently running with a 38 tire. With the 40s Highway speeds weren't bad maybe turning 2000rpms at 70mph. With the the 38s at 70mph its almost 2300. Fuel mileage sucks, I drove across state and hand calculated 20mpg with the 40s, and over all acceleration isn't what it used to be either. So the 4.56 are to tall of a gear for the 38s.

    Couple of choices, regear the axles, or go with a gear vendor overdrive unit. I hAve no experience with the gear vender unit and do t really have many videos on YouTube of real truck reviews. Not sure what to defeat to either. I know there are charts and what not but would like to get some input on these options. What do y'all think???
     
  2. 01yellerCobra

    01yellerCobra Full Access Member

    Messages:
    434
    Likes Received:
    84
    Joined:
    Jul 18, 2015
    Location:
    Cali
    The 4.56's are short gears. Tall gears would be like 3.55's. Think of tall gears having longer legs on the freeway.

    Anyway, I know guys that have run the Gear Vendors set up and have no issues. But you should compare prices between that and regearing the axles. I bet you'll be close. And personally I'd regear the axles.
     
  3. bcvickers

    bcvickers SDD Junior Member

    Messages:
    39
    Likes Received:
    8
    Joined:
    Dec 28, 2008
    Location:
    Minnesota
    You're going to want to go to probably 4.11's to get back to where you were at with the 40's. 2000 rpm at 70mph is the sweet spot for these trucks; too many more rpm's and fuel mileage drops like a rock, too many less and you're waiting on the turbo to spool anytime you get into it. That's how it works with stock engines anyway.
     
  4. patrickc

    patrickc Full Access Member

    Messages:
    722
    Likes Received:
    1
    Joined:
    Dec 8, 2006
    Location:
    Ontario, Canada
    My Dually has 4:10’s. 6.0L diesel, automatic, on 35’s. I run right around 2100 rpm at 70mph, in OD.

    If you ask me 4:56’s are a little too much gear for 38’s. Backing her down to 4:10’s would be choice, should put you back in the 19-2000rpm range.
     
  5. DIESEL JOHN DOE

    DIESEL JOHN DOE SDD Junior Member

    Messages:
    4
    Likes Received:
    0
    Joined:
    May 8, 2021
    Location:
    Tennessee
    well my f350 i have upgraded to a garret turbo hybrid with wicked wheel it is a 96 not the truck in the profile picture
     
    Last edited: Jun 27, 2021
  6. Goneracin

    Goneracin SDD Junior Member

    Age:
    39
    Messages:
    6
    Likes Received:
    0
    Joined:
    Jul 22, 2007
    Location:
    Southington CT
    I run 37 inch tires with 4.30 gears and it put the truck right back to stock gear ratios. It is so close to stock that I actually disconnected my tru-speed spedometer corrector after the gear swap.

    I also use this truck to tow quite a bit, mostly our 8000 lb camper, so towing between 2000 and 2300 rpm is good for me. If you arent towing and want a slightly lower RPM at 80, then a 4.10 will do better for that. Really depends what you use the truck for and how you want to drive it.
     

Share This Page