TNRamGuy
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3.21. vs 3.92 gear
- Thread starter Mike97
- Start date
TNRamGuy
Ram Guru
Yeah, I am so pissed that no matter how much I try, I can not get to single digits for mpg, 10.2 is my personal best for a tank, man that was fun.
IvoryHemi
Ram Guru
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I’ve had real world experience with two very comparable vehicles, towing the same 7,000 lb GVWR camper.
Ram 5.7L/ 8HP75/ 3.92/ 5,700 lbs
Durango 5.7L/ 8HP70/ 3.09/ 5,400 lbs
Both are 4WD, the MDS always off, 89 gas, tires are 30.4” vs 32.1”.
From a dead stop the 3.92 pulls easier, no question. That’s not saying the 3.09 struggled, it just doesn’t feel as effortless.
On the highway not much difference. 3.09 stayed in 6th and never 7th gear, while 3.92 is 7th and rarely sees 8th
Engine breaking with downshifting is significantly better with the 3.92
After 12,000 miles of towing (6k each), overall the 3.92 averaged ~1.5 mpg better than 3.09
Also worth noting, when not towing I averaged ~16.5 mpg with both vehicles. Durango slightly (+0.5 mpg) better
Ram 5.7L/ 8HP75/ 3.92/ 5,700 lbs
Durango 5.7L/ 8HP70/ 3.09/ 5,400 lbs
Both are 4WD, the MDS always off, 89 gas, tires are 30.4” vs 32.1”.
From a dead stop the 3.92 pulls easier, no question. That’s not saying the 3.09 struggled, it just doesn’t feel as effortless.
On the highway not much difference. 3.09 stayed in 6th and never 7th gear, while 3.92 is 7th and rarely sees 8th
Engine breaking with downshifting is significantly better with the 3.92
After 12,000 miles of towing (6k each), overall the 3.92 averaged ~1.5 mpg better than 3.09
Also worth noting, when not towing I averaged ~16.5 mpg with both vehicles. Durango slightly (+0.5 mpg) better
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The 3.92 is rated higher because it is easier on the transmission for warranty purposes, such as ease of accel from stopped, as noted above. The max rating for the frame, brakes, etc would be the same. My son has the same basic truck, except 3.21, and his feels faster than mine unloaded because it spends less "TIME" at reduced power for shifting, and more "TIME" pulling in a gear. Again, mine tows "easier". Ever heard a "tuned" charger (challenger, durango, etc) shift lighning quick? Far less time at reduced power for transmission warranty.
I didn’t read the whole thread, but the 3.92 would preserve more towing capability (not OEM published) and longevity on trucks with bigger diameter tires. Makes sense to start with the gear that would grow with you.
VegasRob55
Active Member
Yup, BS. I use 91 and can't ever do better than 16mpg of combined driving
VegasRob55
Active Member
I have a 2wd Laramie with 3.21 rear axle. I tow a 7,000 lb. recreational trailer up into 10,000' Utah Mountain elevations with zero problems. This is also with about 2,000 lbs. worth people & camping gear in the truck as well. Truck is an absolute beast, bone-stock. No tow pack, basic rear end, 5.7L HEMI, 2WD/Rear Wheel. As basic a setup you can get in a V-8 truck, and can tow tough/max-rated loads at very high elevation (10,000'+) and ultra-high heat (120+ degrees fht)
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You have 2700 lbs of payload? That's pretty good.
Talon4U2NV
Active Member
We just picked up a 2019 Laramie 1500 Sport, It has the 3.92 gears with LSD and we snagged it 'used'. I can say coming from 3/4 and one ton Cummins truck for the past almost 17years... The half ton is a change... but not bad, I love the 3.92 gears so far. The day after the truck came home we hit the road empty and bucked some cross and head winds but averaged 17.5-17.7 MPG running 77-80mph. Only upgrade is a bed cover and we just ran 87 for fuel... I'm pretty happy with the pick up and my back appreciates the ride. We do not have the livestock or big toyhauler anymore and with costs on the rise... I really couldnt justify the 1 ton mega anymore... Though we miss the truck and disposable tow power.. I think this will do just fine.. Hoping this spring to head from Nebraska town to Texas to haul a Mach1 back so curious to see how the truck does.. but i'm happy this far.
JimD007
Active Member
3.92 gears means the driveshaft rotates .71 more of a turn for the axle to rotate once than with 3.21 gears. From a stop, that means more torque since both should be in first gear and the engine in the 3.92 truck will be higher in rpm. But on the highway, unless both trucks are in the same gear, the difference in rear end ratio will not mean the 3.92 truck is higher in rpm. A difference in the transmission ratio can easily make up for the difference in rear end ratio. The truck with 3.92 gears may be turning lower rpm and getting better mileage if the 3.21 truck has to drop down too far in transmission ratio.
Gman
Ram Guru
I haven't read this thread in a loooong time. But here it is, still going.
The 5.7 Hemi produces significant torque, so it's not like the 3.21 equipped trucks start hunting for lower gears at the slightest incline (at least not in my experience with eTorque). If I'm careful with the throttle, I can even maintain the cylinder deactivation with a bit of load.
A 3.92 is not going to turn more revs and be more fuel efficient. It's just physics. The 3.92 provides better mechanical advantage but it does so at the cost of more revolutions per linear distance. All things being equal, more revs equals more fuel consumption over the same distance.
www.autolist.com
The 5.7 Hemi produces significant torque, so it's not like the 3.21 equipped trucks start hunting for lower gears at the slightest incline (at least not in my experience with eTorque). If I'm careful with the throttle, I can even maintain the cylinder deactivation with a bit of load.
A 3.92 is not going to turn more revs and be more fuel efficient. It's just physics. The 3.92 provides better mechanical advantage but it does so at the cost of more revolutions per linear distance. All things being equal, more revs equals more fuel consumption over the same distance.
Axle Ratio - Where to Find It and Which Is Best For You?
Understanding axle ratios is easier than you may think, and is critically important to making sure your vehicle meets your needs.
www.autolist.com
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I haven't read this thread in a loooong time. But here it is, still going.
The 5.7 Hemi produces significant torque, so it's not like the 3.21 equipped trucks start hunting for lower gears at the slightest incline (at least not in my experience with eTorque). If I'm careful with the throttle, I can even maintain the cylinder deactivation with a bit of load.
A 3.92 is not going to turn more revs and be more fuel efficient. It's just physics. The 3.92 provides better mechanical advantage but it does so at the cost of more revolutions per linear distance. All things being equal, more revs equals more fuel consumption over the same distance.
Axle Ratio - Where to Find It and Which Is Best For You?
Understanding axle ratios is easier than you may think, and is critically important to making sure your vehicle meets your needs.
ferraiolo1
Spends too much time on here
Idk what that proves only averaging 33 mph
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Sent from my iPhone using Tapatalk
TNRamGuy
Ram Guru
Good city mpg for a 5.7!?
ferraiolo1
Spends too much time on here
Took over two hrs to drive 74 miles. That’s an odd scenario. If so that’s a lot of stop and go traffic.
Can’t wait to see that screen and 400 miles.
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Can’t wait to see that screen and 400 miles.
Sent from my iPhone using Tapatalk
Don't see any 3.21s hitting 28.2mpg with a Hemi, regardless of speed, distance, or length of time.
So not only do you have weak gears that can't pull anything, you also have a gas guzzler.
So not only do you have weak gears that can't pull anything, you also have a gas guzzler.
ferraiolo1
Spends too much time on here
I can hit 32mpg going down hill for 74 miles.
Sent from my iPhone using Tapatalk
Sent from my iPhone using Tapatalk
If I was going downhill I might have broke 50mpg with these 3.92s.
VegasRob55
Active Member
Well saidI haven't read this thread in a loooong time. But here it is, still going.
The 5.7 Hemi produces significant torque, so it's not like the 3.21 equipped trucks start hunting for lower gears at the slightest incline (at least not in my experience with eTorque). If I'm careful with the throttle, I can even maintain the cylinder deactivation with a bit of load.
A 3.92 is not going to turn more revs and be more fuel efficient. It's just physics. The 3.92 provides better mechanical advantage but it does so at the cost of more revolutions per linear distance. All things being equal, more revs equals more fuel consumption over the same distance.
Axle Ratio - Where to Find It and Which Is Best For You?
Understanding axle ratios is easier than you may think, and is critically important to making sure your vehicle meets your needs.
