Next, rear end gearing

Discussion in 'GM Powertrain' started by vannooch, Oct 16, 2011.

  1. vannooch

    vannooch Rockstar

    After deciding against the stroker engine, I am considering a rear end gearing change. Currently, I have 3:73 locking differential and my question is can I change this to a 4:88 locking differential? Should I consider this, it seems like it would really give me the bottom end torque I would like to have. It may tow fine with the new engine but I would like to get that little bit extra.
     
  2. Crawdaddy

    Crawdaddy ↑↑↑ Has no life Staff Member 5+ Years 1000 Posts Platinum Contributor

    Unless you're moving up to 35" or taller tires, I wouldn't recommend anything more than 4.10s. And the 4.10s probably won't feel much different than the 3.73s, so I probably wouldn't bother regearing.
     
  3. TELORVEHC

    TELORVEHC Rockstar 4 Years 1000 Posts

    Not really worth it unless you plan on moving considerably larger tires. You could probably get more of that bottom end torque you're looking for with an intake and exhaust compared to re-gearing.
     
  4. Boonduff

    Boonduff Member 3 Years 100 Posts

    Hope you realize that with the size tires you have on that van with 4.88s your top speed will probably be 45mph in overdrive.
     
  5. vannooch

    vannooch Rockstar

    I would likes to change tire size at some point I don't know what will fit under there. The reason for the post is that I was looking for towing torque. I pull a 5500 lb travel trailer but it may be fine with the fresh engine being installed over the next couple of weeks I just don't know much about rear end gearing and the associated response affects. So I thought I would research a little. So I'm gathering that 4.88's are for large tires only. A rear end gear change isn't to gain torque.
     
    Last edited: Oct 18, 2011
  6. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner Gold Member 1000 Posts

    In your setup the 4.88's would give you bad fuel economy as the engine will be revving alot higher at lower speeds. As Crawdaddy said with your stock tires you could do 4.10's. I know with my truck in its stock setup the manual said that the truck with 4.10's rather than the stock 3.73's added 1000 pounds to the towing capacity, so that is an option since you are looking towing purposes. If you got close to 33" inch tires (since you said you may go bigger the 4.10's would get you back to an effective gear ratio close to that of the stock setup).

    ---------- Post added at 10:02 AM ---------- Previous post was at 09:55 AM ----------

    Also if its the g80 you can do the 4.10's or 4.56 and only change the gears (the g80 locker wouldnt need to be changed). depending on the housing 4.88's may not even fit. And to add what I mentioned before on the tires if you went with a tire close to a 33" (not sure if it would fit) then even a 4.56 would give you that lower gear ratio you may be looking for, but I probably wouldnt go that short of a gear unless you went bigger tires.
     
  7. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    I wouldn't go over 4.10's with that size tire. MAYBE 4.56's if you go to a taller tire.
     
  8. Marcus A.

    Marcus A. Rockstar

    I've looked into gears alot. A set of 4.56 with 33' tires will have a very close speed to rpm ratio as that of 4.10 with 31" tires. I have 33" tires with 3.73 and it causes my speed to act s if I had 3.42 gears with 31" tires. My towing cap. is cut down so bad it hurts to pull my 5k camper up any hill or run OD down the highway. I made a spread sheet in Exel that can calculate mph in each gear by entering trans gear ratios, engine rpm, tire size. Fun to play around with. Here it is with a 4l80e trans. This would be with the lock up converter locked.
    [TABLE="width: 516"]
    [TR]
    [TD="class: xl32, width: 56, bgcolor: transparent"]Engine RPM[/TD]
    [TD="class: xl25, width: 20, bgcolor: transparent"][/TD]
    [TD="class: xl36, width: 51, bgcolor: yellow"]2300[/TD]
    [TD="class: xl25, width: 51, bgcolor: transparent"][/TD]
    [TD="class: xl25, width: 51, bgcolor: transparent"][/TD]
    [TD="class: xl24, width: 51, bgcolor: transparent"][/TD]
    [TD="class: xl24, width: 51, bgcolor: transparent"][/TD]
    [TD="class: xl24, width: 51, bgcolor: transparent"][/TD]
    [TD="class: xl24, width: 51, bgcolor: transparent"][/TD]
    [TD="class: xl24, width: 153, bgcolor: transparent, colspan: 3"]Tire Size & Radius[/TD]
    [TD="class: xl24, width: 51, bgcolor: transparent"][/TD]
    [TD="class: xl24, width: 54, bgcolor: transparent"][/TD]
    [/TR]
    [TR]
    [TD="class: xl28, bgcolor: transparent"] [/TD]
    [TD="class: xl39, bgcolor: transparent, colspan: 2"] [/TD]
    [TD="class: xl28, bgcolor: transparent"] [/TD]
    [TD="class: xl33, bgcolor: transparent"]Rear End [/TD]
    [TD="class: xl33, bgcolor: transparent"] [/TD]
    [TD="class: xl29, bgcolor: transparent"] [/TD]
    [TD="class: xl29, bgcolor: transparent, colspan: 2"]Axle RPM[/TD]
    [TD="class: xl29, bgcolor: transparent"] [/TD]
    [TD="class: xl34, bgcolor: yellow, align: right"]33[/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [/TR]
    [TR]
    [TD="class: xl41, bgcolor: transparent, colspan: 4"] [/TD]
    [TD="class: xl35, bgcolor: yellow"]4.56[/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl31, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"]103.67[/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"]MPH[/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [/TR]
    [TR]
    [TD="class: xl30, bgcolor: transparent"]1st Gear[/TD]
    [TD="class: xl30, bgcolor: transparent"][/TD]
    [TD="class: xl26, bgcolor: transparent"]2.48[/TD]
    [TD="class: xl25, bgcolor: transparent"]:1[/TD]
    [TD="class: xl26, bgcolor: transparent"]11.309[/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"]203.38[/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl37, bgcolor: transparent"]19.967[/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [/TR]
    [TR]
    [TD="class: xl30, bgcolor: transparent"]2nd Gear[/TD]
    [TD="class: xl30, bgcolor: transparent"][/TD]
    [TD="class: xl26, bgcolor: transparent"]1.48[/TD]
    [TD="class: xl25, bgcolor: transparent"]:1[/TD]
    [TD="class: xl26, bgcolor: transparent"]6.7488[/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"]340.8[/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl37, bgcolor: transparent"]33.458[/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [/TR]
    [TR]
    [TD="class: xl30, bgcolor: transparent"]3rd Gear[/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl26, bgcolor: transparent"]1[/TD]
    [TD="class: xl25, bgcolor: transparent"]:1[/TD]
    [TD="class: xl27, bgcolor: transparent"]4.56[/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent, align: right"]504.39[/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl37, bgcolor: transparent"]49.518[/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [/TR]
    [TR]
    [TD="class: xl30, bgcolor: transparent"]4th Gear[/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl26, bgcolor: transparent"]0.75[/TD]
    [TD="class: xl25, bgcolor: transparent"]:1[/TD]
    [TD="class: xl26, bgcolor: transparent"]3.42[/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"]672.51[/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl27, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl24, bgcolor: transparent"][/TD]
    [TD="class: xl37, bgcolor: transparent"]66.024[/TD]
    [TD="class: xl38, bgcolor: transparent, align: right"]66[/TD]
    [/TR]
    [/TABLE]
     
  9. Marcus A.

    Marcus A. Rockstar

    with 31" tires (245/75R16) you will have a speed of 62 with the same rpm and gear ratio. It will multply the torque to the wheels but limit top speed and kill fuel milage. That being said at 3000 rpm you'd be doing around 80 mph. Enough to get a speeding ticket. I don;t do much more than 65 not towing and under 65 towing.
     

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