Real world difference between 3.21 & 3.55?

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Jeepwalker

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Just curious your thoughts for guys who have either the 3.21 and 3.55 gears? Esp for the V6.

-Fuel economy
-General ownership (acceleration/passing, etc)
-Towing

Thx!
 

caulk04

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9.5%.

With the 8spd, the 3.21 isn't terrifying as many people think it is. That said, I'd still prefer the shorter option (3.92 for me). Much of my driving is 60 and below so I reap less advantage from the tall gears.

If you're going to tow often, get the shorter gear.

If you're going to drive mostly rural/city, get the shorter gear.

If you plan to increase tire size, get the shorter gear.

If you travel mostly highway, the taller gear will get you a little better mileage.
 

Wild one

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Just curious your thoughts for guys who have either the 3.21 and 3.55 gears? Esp for the V6.

-Fuel economy
-General ownership (acceleration/passing, etc)
-Towing

Thx!
I went from 3.21's to 3.55's and noticed a fair milege drop,but then again,most of my driving is on the freeway at 80+ mph,my oil temps also increased noticably. Around town i don't really notice as much differance though. I also didn't gain squat at the dragstrip with the 3.55's,with the 5.7 i wouldn't do it again. I prefer the 3.21's over the 3.55's,but i don't tow,and i also don't have a V6 Jeep. With the little 3.6 they might be worth having though.
 

gfh77665

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I was referring to the V6, like the OP requested.
 

RLJ10X

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Several years ago, there was a new guy on this forum who had (I think) had a RCSB, 2WD, V6, 8 Speed. <That was a cool combination, BTW. Anyway, he took it to his local dealership and had a 4.10 gear put in. I was really looking forward to hearing his thoughts on his truck.

He drove his truck once or twice, and was really happy with it. This is where the story gets weird.... Like I said, he drove the truck once or twice and the dealership said "They had to have that truck". So the dude trades his newly re-geared truck for a 10 speed Mustang. You have to wonder about a guy who goes to a dealership to get his truck re-geared and comes home with a new car.

Anyway, I always wondered how a V6 would respond to 3.92, or better yet 4.10.
 

rvance

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I have had both in V6 trucks and I much prefer the 3:55. With the 3:21 it only goes into 8th downhill with a tailwind. Many trips I don't think it gets into 7th. I got better gas mileage with the 3:55 too.
 

Marine Les

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I have 3.55s w/v6 and want the 3.92s. Rebel trucks w/v6 come with 3.92s and report mpg numbers similar to the 3.21/3.55 gears. I must do 70 to get into 8th and do not normally drive that fast.
 

JetDoc

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I have the EcoDiesel V-6 with 3.55 gears in my Ram 1500 4x4. The truck gets amazing fuel mileage for a full-size 4x4 and can still tow nearly 8000 lbs over the mountain passes like the trailer wasn't there.
 
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Jeepwalker

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I have had both in V6 trucks and I much prefer the 3:55. With the 3:21 it only goes into 8th downhill with a tailwind. Many trips I don't think it gets into 7th. I got better gas mileage with the 3:55 too.
I have 3.55s w/v6 and want the 3.92s. Rebel trucks w/v6 come with 3.92s and report mpg numbers similar to the 3.21/3.55 gears. I must do 70 to get into 8th and do not normally drive that fast.

Good points, guys. I never thought about those factors.

_
 

bisonfan

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I just bought a 16/V6/CC/3.55/17" outdoorsman 5 days ago. I am still learning the truck from all aspects...

A few things I have noticed:

-Saturday night I drove into a 30mph wind. Truck held 8th gear on flat and would shift to 7th on inclines at 60-63 mph. I was surprised I expected 7th gear the whole way. (3 adults and two teens with a few items under the Tonneau cover)
-Driving home from the dealer two hours away, I put on 55 miles at 75mph... I average 17.5, once I slowed downed to 60 or 65 it shot up to near 19 or so combined with the interstate driving.
-Since Saturday night I have put on 50 miles in city/rural driving and am averaging 17.8 mpg. 70% city/30% rural 55mph roads
-I find best acceleration between 2000 & 2700 rpm
-The 8 speed is a magic box

I did not look at the 3.21 ratio as I intend to pull a 2 or 4 place aluminum trailer with atv's on it and wanted the 7000lb towing capacity.

I spent the last two months looking/deciding between the Hemi 3.21 and Pentastar 3.55 setup. I ultimately chose the V6/3.55 due to the reliability of the v6. I have nearly 200K miles experience with a 2012 DGC and 2015 T&C and never had a single problem with them. I wanted the same for my truck that I want to keep for a minimum of 10 years. My truck did have a cracked oil filterhousing that the dealer repaired before putting on the lot. Valvetrain sounds normal upon startup so I felt comfortable that it was not damaged.
 
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Jeepwalker

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Bisonfan:
I just bought a 16/V6/CC/3.55/17" outdoorsman 5 days ago. I am still learning the truck from all aspects...

Sounds like a sweet truck. And good economy for a large tk. Thanks for sharing your real-world feedback. Is that 2-by or 4x4?
 

turkeybird56

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Several years ago, there was a new guy on this forum who had (I think) had a RCSB, 2WD, V6, 8 Speed. <That was a cool combination, BTW. Anyway, he took it to his local dealership and had a 4.10 gear put in. I was really looking forward to hearing his thoughts on his truck.

He drove his truck once or twice, and was really happy with it. This is where the story gets weird.... Like I said, he drove the truck once or twice and the dealership said "They had to have that truck". So the dude trades his newly re-geared truck for a 10 speed Mustang. You have to wonder about a guy who goes to a dealership to get his truck re-geared and comes home with a new car.

Anyway, I always wondered how a V6 would respond to 3.92, or better yet 4.10.
HEY, in 2009, I took wife's 4.6L 2 valve F150 4 X 4 to the dealer for service. I came home with a Brand new 2010 F150 4 X 4 with the 5.4 Triton motor, easy to do, LOL.
 

Burla

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3.55's worst thing about my truck, but I guess because I have an rfe it is not the same. However when you go from gear sets in the 3's to the 4's, you can see the benefit with any load.

3.73 versus 4.10 - there ya go. Almost the same increase as 3.21 to 3.55, but as you can see the size of the gears are gonna benefit you under any load. Point being, if you wanna play with gearing, I believe the saying is go big or....

373-vs-410-gears_a8ba5e32.jpg
 

TomB 1269

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The math says better gas mileage, and the may be true in a test environment, but I know my 2019 w/ 5.7 likes to 7/8 swap with any change in grade. Also with high winds it does not like to go higher than 7th.
With 3.55 I would assume I would see better mileage in general as it would start off the line better and the rpm change at speed would not be that great but just enough the truck would most likely run in 8th vs the 7/8 swap hunt it does with any change in grade or aero-forces on the front end. i.e. 15/20 MPH head on gust of wind
 

bisonfan

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The math says better gas mileage, and the may be true in a test environment, but I know my 2019 w/ 5.7 likes to 7/8 swap with any change in grade. Also with high winds it does not like to go higher than 7th.
With 3.55 I would assume I would see better mileage in general as it would start off the line better and the rpm change at speed would not be that great but just enough the truck would most likely run in 8th vs the 7/8 swap hunt it does with any change in grade or aero-forces on the front end. i.e. 15/20 MPH head on gust of wind

The math says better gas mileage, and the may be true in a test environment, but I know my 2019 w/ 5.7 likes to 7/8 swap with any change in grade. Also with high winds it does not like to go higher than 7th.
With 3.55 I would assume I would see better mileage in general as it would start off the line better and the rpm change at speed would not be that great but just enough the truck would most likely run in 8th vs the 7/8 swap hunt it does with any change in grade or aero-forces on the front end. i.e. 15/20 MPH head on gust of wind
I would concur with this logic for the most part. I am surprised the 5.7 would 7/8 swap with extra torque it has. Mine jumps on slight grade but the jump is only 400 times and u can hardly notice it.
 

Wahrsuul

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What wheel sizes are you running with the 3.55? I'd think you'd want the 3.55 with the 20" wheels.
 

RLJ10X

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It takes a certain amount of energy to shove a big pick-up thru the air and overcome rolling resistance. There's no way around that. If taken to the extreme, if you wanted, you could gear so tall, the engine would have to work a lot harder, thus using more fuel, at low rpms. Or you could gear so low, the engine is spinning like crazy, with light throttle application, because there is very little load on the engine. But somewhere in the middle of all that, is balance. That's why guys with 3.92s get about the same gas mileage as the 3.21 owners. RPM are not the only factor in the equation.

3.21s are in most trucks for emissions and carbon credits. Simple as that.
 

Dusty

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3.55's worst thing about my truck, but I guess because I have an rfe it is not the same. However when you go from gear sets in the 3's to the 4's, you can see the benefit with any load.

3.73 versus 4.10 - there ya go. Almost the same increase as 3.21 to 3.55, but as you can see the size of the gears are gonna benefit you under any load. Point being, if you wanna play with gearing, I believe the saying is go big or....

View attachment 492974
Which gearset do you believe is the stronger, left or right in the picture?

Regards,
Dusty
2019 Ram 1500 Billet Silver Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 3 June 2018. Now at 69718 miles
 
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