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80 Seies Revs with 4.8 diffs

Discussion in '80-Series Tech' started by Red Rover, Aug 26, 2006.

  1. Red Rover

    Red Rover

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    Hi,

    I run an 96 4.5 auto with 285 x 75 x 16's. It only seems 4.8 diffs are only available, can anyone tell me what revs it would do say 100 km per hour (60 mph)

    any help appreciated
     
  2. kennyv0826

    kennyv0826

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    Please clarify your question I'm not clear exactly what you're asking?
     
  3. SOCALFJ

    SOCALFJ

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    are you talking about your ring and pinion? 4.88's?

    im confused too. :confused:
     
  4. Red Rover

    Red Rover

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    Sorry, yep talking anout ring and pinion. I need to regear the diffs for better towing etc, however I am really unsure about what ratio. Most of the time I run 285 x 75 x 16 tyres (33inch equivelent). I would have thought that 4.3 or 4.5 ratio would be spot on (only because I had a Nissan Patrol running the same tyres and it was good with 4.3 diffs). However having a look on the web it only seems that 4.8 ratios are only available now (as the tallest ratio anway) I also saw a few blokes here run them and say they are good but I am concerned it will rev it's nut off at highway speeds. Although this is my first 4wd auto so maybe its a little different.

    So I guess my question is what revolutions is the engine doing at 60mph (100kph) with 4.8 diffs and 33 inch tyres (285's)

    Thanks guys
     
  5. landtank

    landtank SILVER Star

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    well, not knowing what your tranny gearing is it would be hard to just give you an accurate number. You could easilly calculate the % difference in gearing and then apply that % to your own RPMs at 100kph.

    Over here the stock ratio is 4.11 and you are saying you are looking at a new ratio of 4.88. That would yield a 16% increase in RPMs. So drive the truck at 100kph and then multiply the RPMs by 1.16 to get the RPMs at the new gearing of 4.88.
     
  6. airlaird

    airlaird

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    Red Rover, send me your 4:88's and I'll send you my 4:56's.
    airlaird
     
  7. Red Rover

    Red Rover

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    I'd imagine transmission gearing would be the same as you blokes. Yep runs 4.11. MMMM when a guys says he wants to change from 4.5's to 4.8's it says to me that 4.8's are the go. 16% will bring it around 2100 rpm as I do about 1800 rpm now. I calculated it at about that with ratio calculators but though jumping from 4.11 to 4.8's would increase it more, but there you go.

    Thanks guys
     
  8. kennyv0826

    kennyv0826

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    I'm guessing that 4.88 gearing would work out very well for you.
     
  9. -Spike-

    -Spike-

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    Most people regear when they add larger diameter tires- 35" and up. Airlard probably is running bigger tires and wants the higher ratio for that reason. Running stock size tires, I'd think 4.56:1 would be plenty for some towing, but that's just my opinion. If you're not gonna go over 100kph, you could probably run 5.1x:1. I guess it depends on how much towing, how much weight, what speeds you'd like to run regularly, and so on.

    -Spike
     
  10. landtank

    landtank SILVER Star

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    We have two different autos here in the states and no manual is available. All three have different ratios. With the tires you are running I don't think anyone has bothered to regear, with 35" tires 4.56 gears return the vehicle to stock and the more widely choice is 4.88s to end up a little lower than stock.
     
  11. Panzer

    Panzer SILVER Star

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    That guy is currently running 37' tires and needs to jump to 4.88's
    (Not a dig Steve, just clarifying things to our southern brother.)

    For 285's I would go with 4.56
    315 + I'd do 4.88

    My 0.02
    CAS
     
  12. kennyv0826

    kennyv0826

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    I think I am going to run 5.29's when I put on the 37's. I could prolly get away with 4.88's because I'm not going to tow anything but I would rather have the extra torque on and off road.

    With 33" tires 4.56's are prob enough but it depends on how weight much you tow and how many (and steep) hills you are running up. If you aren't going to ever put bigger than 33's you may want to stick with 4.56's instead of 4.88's.
     
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