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What Gears for 38.5 Swappers?

Discussion in 'The Garage' started by BANKO, May 31, 2002.

  1. BANKO

    BANKO Registered Member

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    Sunnyvale, CA
    What gears are you running with 38" tires. I assume most are running 4.56 or taller with their SB 350 engines and overdrive transmissions. I currently have a 454, th400, and 4:10 gears in my K20. I eventually want to go to 38s but it struck me that I might have to change my gears as well. What do you think?

    -Josh
     
  2. fulltopblazer

    fulltopblazer 1/2 ton status

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    I would go with 4.88 or5.13 depends what you do with it. when I switch to 39.5 boggers I'm going with 5.13 but I need a D60 first and about a million $$$$$$$
     
  3. 91K5

    91K5 1/2 ton status

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    If you have 35's with 4.10 now, stepping up to 38" and swapping to 4.56 gears would be about the equivelent as to what you have currently. If you plan to drive highway the 4.88's would be as steep as I'd go and keep the engine RPM's livable. With the 454 motor you could probably stay with 4.10's and not notice much difference with that much torque though.
     
  4. 72THING

    72THING 1/2 ton status

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    I have 39.5" Swampers and 4.56 gears with a 4-speed and basically stock 355. I can pull second gear high range through the mud if it isn't too awful deep and get monstrous wheel speed. On the highway, my engine is at about 2400 RPM at 60 MPH. With your big block, you'll probably be fine with the 4.10s, but if you go lower, I wouldn't go any lower than 4.88.

    Will
     
  5. chvyhs

    chvyhs 1/2 ton status

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    What I did was looked at the tire/gear calculator on the 4WPs site. I found my old tire, gear, and rpm's. Then found what matched my new 38's. My engine is getting tired so I went with 4.88's. They're on order right now so I wont be able to tell you how well things worked out for a while.
     
  6. BorregoK5

    BorregoK5 1/2 ton status

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    I'm running 4.56's on a 415ci / th350 with my 38.5's. The gas mileage is good, runs about 2800rpm on the freeway at freeway speeds (california). Good power and low range on an np203 is decently slow and torquey. I could live with 4.88's just as easy though and would consider it a toss up as to which to get... 4.56 with a torquey motor for more daily driving / 4.88's for more off road oriented trucks or less torque / and into the 5's with a trail only rig regardless of motor. All this is based on the 3 speed auto, your 400 has a longer first geer so 4.56 might seem a little slower off the line and crawl a little faster in 4 low but with the torque your big block puts out, I doubt you'd notice the difference. I can line lock the 38's and roast them, or punch it and get them spinning for a couple of feet. Hope this helps.
     
  7. NITRO

    NITRO 1/2 ton status

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    im runnin 3.72 rear with 44" boggers and 3.42 front with 37" boggers on the 555ci. these are in 10 and 12 bolt chromoly axles. i even still have c-clips and havent broke one yet. but then again this is on my '79 mud bogg/drag truck. other than that i run 4.56 in my 1 ton axles that i swap out for other shows with 38" boggers.

    NITRO
     

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