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Thread: Next, rear end gearing
10-16-2011, 08:51 PM #1
Next, rear end gearing
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.2001 GMC Savana SLT
10-16-2011, 10:12 PM #2
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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.Christopher
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10-16-2011, 10:32 PM #3
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.04 ECSB Custom silver & grey, Soft 8's, BFG KO's, ReadyLift Leveling Kit, Hellwig front sway bar, K&N filter, DeeZee EZ-Down, Rhino liner, Alpine CDE103BT, Rockford 6.5's, 12" V.A.T. Hammer Pro in a Subthump box, Alpine PowerPack amp, Hifonics amp, BackRack w/ 55w 5000k HID KC Daylighters, KC light bar with 4 KC Slimlites, UWS toolbox, Shaved Antenna mod, Black Bowtie, LED backup, license plate, dome lights & 3rd brake light
10-18-2011, 01:41 AM #4
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.
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10-18-2011, 06:16 AM #5
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 by vannooch; 10-18-2011 at 06:20 AM.
10-18-2011, 01:02 PM #6
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.David
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10-19-2011, 01:58 PM #7
I wouldn't go over 4.10's with that size tire. MAYBE 4.56's if you go to a taller tire.:cool:
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10-25-2011, 08:08 PM #8
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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.
Engine RPM 2300 Tire Size & Radius Rear End Axle RPM 33 4.56 103.67 MPH 1st Gear 2.48 :1 11.309 203.38 19.967 2nd Gear 1.48 :1 6.7488 340.8 33.458 3rd Gear 1 :1 4.56 504.39 49.518 4th Gear 0.75 :1 3.42 672.51 66.024 662003 Suburban 2500 LT, 6.0l Volant cai. 3.73 gear. Mobil 1 syn oil
10-25-2011, 08:13 PM #9
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- Central PA
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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