4.56 or 4.88 w/ 6.4

[FlatbedHemi]

I know there are a couple threads on this topic, but I didnt want to hijack those threads with a slightly different, but specific question, so I will start my own.

Getting closer to making the swap to lower gears, but for the life of me I cannot decide which set to go with. I am looking at 4.56 and 4.88 options. I am currently running 3.73s with 34” tires, getting roughly 12-14 MPG (EVIC) depending on which seasonal blend of fuel is available. That’s unloaded and running about 75mph.

I know the gears in either ratio will be a huge upgrade, and I know that a lot of you guys are proponents of the 4.88 from a performance standpoint, but what about fuel mileage? Yeah, I know, Its not a Prius. But, since most of my driving is 20-30 mile+ stretches of highway driving I would like some real world comparison of fuel mileage for each gear set. I know each set has potential to improve my mileage by allowing the engine to work less by keeping it in the power band, taking less throttle to accelerate, as well as letting the engine run in ECO more often. But, at so e point there has to be a point of diminishing return. If both sets will net about the same MPG, then I will go 4.88, but if 4.56 has better economy, it might be worth it to leave some torque on the table for the sake of highway MPG. I just need some real world numbers for comparison.

Since I cant really afford to try one gear-set then the other, I would like to ask anyone who has done the 4.56 or 4.88 swap to post your fuel mileage on stock gears and on the new gears. If I can get some input I certainly would appreciate it, and it will help me make up my mind.

OR, if anyone that sees this lives in or is traveling through east Texas and wouldn’t mind letting a stranger test drive, that would be great too.

 

[tjfdesmo]

Spicer has a couple good RPM and speed calculators on their site.
https://spicerparts.com/calculators/engine-rpm-calculator

If you fool with them a while, and can determine the closest stock ratio to where you'd end up as a final overall ratio you could lock you trans to that gear and do a test run with your truck. I have not done the math, so it might not work out as close enough, but it's a place to start.

Honestly, if you are doing this just to gain a little MPG, I doubt it will be worth it in the long run.

 

[olyelr]

IMO you are not gonna get very far with your specific question. MPG numbers are all over the board even with stock trucks. Some claim to get a steady 12, some claim to get 15-16 no prob. Im guessing if you actually found two people running the different gear sets, you would get mixed numbers as well.

My opinion is MPG numbers are not gonna change drastically between 4.56’s or 4.88’s. I mean, what, a half to 3/4’s of a mile at best? Its probably a mute point.

IMO, if you are at all considering 4.88’s, then just go with those.

 

[22hemi13]

34”s aren’t that big. Stock is 33”. A flatbed weighs more than a regular bed..... not counting what tool and gear you’re actually carrying on it. I’d say that has more to do with your mpg than the gearing at this point. Have you scaled your truck how you run it for curiosity’s sake? Obviously a gear change will help some “the actual ratio I don’t know sorry for no help there,” but in the end I’d think your overall weight is your biggest factor. I could be wayyu off just good for thought. FYI I have a 2014 with the 5.7 cclb 35”mud tires 3” lift weight 7650lbs I think roughly if I remember right and get about 12-13mpg mixed highway/city here in southern az. When I lived in hill country tx 11mpg was average and if I had a gooseneck empty or loaded I was 7-8mpg

 

[FlatbedHemi]

Spicer has a couple good RPM and speed calculators on their site.
https://spicerparts.com/calculators/engine-rpm-calculator

If you fool with them a while, and can determine the closest stock ratio to where you'd end up as a final overall ratio you could lock you trans to that gear and do a test run with your truck. I have not done the math, so it might not work out as close enough, but it's a place to start.

Honestly, if you are doing this just to gain a little MPG, I doubt it will be worth it in the long run.

Yeah, I have done all that. And, I am wanting to do it for drivable sake, but I dont want to drop a ton of cash on something like this and leave some performance on the table if the 4.56 isnt gonna give me any more mog than the 4.88, and at the same time I am willing to sacrifice a little torque if I can pick up a couple MPG.

 

[FlatbedHemi]

IMO you are not gonna get very far with your specific question. MPG numbers are all over the board even with stock trucks. Some claim to get a steady 12, some claim to get 15-16 no prob. Im guessing if you actually found two people running the different gear sets, you would get mixed numbers as well.

My opinion is MPG numbers are not gonna change drastically between 4.56’s or 4.88’s. I mean, what, a half to 3/4’s of a mile at best? Its probably a mute point.

IMO, if you are at all considering 4.88’s, then just go with those.

Yeah, I know its all variable. That’s why I am looking for comparison of their own numbers of stock vs. regeared. If I can get enough information from enough members, maybe I can identify a trend that will help me to decide if the difference in mileage is worth leaving the torque on the table. If the difference seems negligible, then Ill do 4.88s.

 

[FlatbedHemi]

34”s aren’t that big. Stock is 33”. A flatbed weighs more than a regular bed..... not counting what tool and gear you’re actually carrying on it. I’d say that has more to do with your mpg than the gearing at this point. Have you scaled your truck how you run it for curiosity’s sake? Obviously a gear change will help some “the actual ratio I don’t know sorry for no help there,” but in the end I’d think your overall weight is your biggest factor. I could be wayyu off just good for thought. FYI I have a 2014 with the 5.7 cclb 35”mud tires 3” lift weight 7650lbs I think roughly if I remember right and get about 12-13mpg mixed highway/city here in southern az. When I lived in hill country tx 11mpg was average and if I had a gooseneck empty or loaded I was 7-8mpg

Never put it on the scale, but I calculated it to around 1300 lbs from materials used to build it. It cost me 1/2mpg over the stock bed. The tires cost me 1-2 depending on time of year.

 

[AFMoulton]

Go 5.13’s. @U&A swapped his 3500 6.4 Hemi to 4.88/4.56s(can’t remember which)and has a thread on here somewhere about his experience. This difference between 4.88/4.56 is sooo small it’s almost not worth comparing. I plan to do 4.88’s, because that is the best for the tire I Run and what I want to do.

This truck with 4.10s and heavy tires gets me on avg 15.1 MPGs around town. And roughly 16-18 on the highway.


2018 2500 6.4 4x4 4.10 Amsoil SS 0w-40, Softopper
Black Rhino Armory 18x9 +12mm
Cooper St MAXX LT295/70R18

2016 Durango 5.7 AWD 3.07 Amsoil SS 4 Qts 5W-30 and 3 Qts 0W-40
1996 Nissan Altima 2.4 Amsoil SS 5W-30

 

[AFMoulton]

6.4 hemi, 4.56 gears, speed and RPM's
https://r.tapatalk.com/shareLink?sh...6-gears,-speed-and-RPM's.109503/&share_type=t


2018 2500 6.4 4x4 4.10 Amsoil SS 0w-40, Softopper
Black Rhino Armory 18x9 +12mm
Cooper St MAXX LT295/70R18

2016 Durango 5.7 AWD 3.07 Amsoil SS 4 Qts 5W-30 and 3 Qts 0W-40
1996 Nissan Altima 2.4 Amsoil SS 5W-30

 

[G. Mcpherson]

Grimmjeeper.com has a good calculator also.

 

[FlatbedHemi]

Yes, I have searched and read all the forum threads, and have played with the calculators plenty. I guess the question that I am wanting answered is a question of which RPM is the engine going to run most efficiently. Will it be more efficient at 1900 RPM, or 2100 RPM? Is the difference negligible? Will the MDS kicking in at 2100 actually be more efficient than if it kicks in below 1900? These are the questions that bear asking in my mind. I am less concerned with performance (as either one will be a huge upgrade) as I am trying to squeeze out ever MPG I can out of this honking behemoth of a vehicle.

Call me crazy, but those are my concerns.

 

[AFMoulton]

Well to address those concerns, I would shut MDS off, either by going into mania l mode or possibly getting it tuned out of the engine, as MDS lifters are a huge failure point in these engines.

The MPG I quoted above is with MDS off. And my 295/70R18 Cooper ST Maxx tires weigh 71lbs each, plus the wheels I have it’s a 92lb mass at each corner.

Granted I have 4.10s and I see 1700-1900 RPM in 6 gear at 60 MPH, I am going 4.88/5.13s mainly because of the weight of my tires, and the fact that I might go bigger tires. I have not decided yet because I plan to level it with Thuren suspension and get a little bigger tire, once I do that I will make my decision on gears.

Hopefully @U&A will jump in with his gas mileage experience from 3.73 to 4.88.

The 6.4 loves 2200-2500 RPM, that’s where I see the best efficiency of everything


2018 2500 6.4 4x4 4.10 Amsoil SS 0w-40, Softopper
Black Rhino Armory 18x9 +12mm
Cooper St MAXX LT295/70R18

2016 Durango 5.7 AWD 3.07 Amsoil SS 4 Qts 5W-30 and 3 Qts 0W-40
1996 Nissan Altima 2.4 Amsoil SS 5W-30

 

[RAM_Designs]

Going from 3.73 to 4.56 gears at 75mph will take you from ~1700rpm to ~2100rpm. IMO, in east Texas driving (I'm in Rockwall, just easy of Dallas), that's the perfect rpm...especially since you're not lifted and running heavier tires. I have 36.5's with the Power Wagon suspension, so there's more wind resistance and rolling weight on each wheel hub to account for...4.88's are perfect for me, and I can run 80mph at around 2300rpm which is about as high as I would like to take it for extended periods of time. At 75mph I'm right around 2150 and it's perfect for me.

IMO 4.88's and especially 5.13's on anything under a 35" tires, is just too high of rpms. I guess if you're at 5k+ elevation and run a lot of mountains where the speed limit is 55-60...but down here 70mph is slow on the highway, and driving down to San Marcos the tollway that detours you around Austin has an 85mph limit.

 

[AFMoulton]

Going from 3.73 to 4.56 gears at 75mph will take you from ~1700rpm to ~2100rpm. IMO, in east Texas driving (I'm in Rockwall, just easy of Dallas), that's the perfect rpm...especially since you're not lifted and running heavier tires. I have 36.5's with the Power Wagon suspension, so there's more wind resistance and rolling weight on each wheel hub to account for...4.88's are perfect for me, and I can run 80mph at around 2300rpm which is about as high as I would like to take it for extended periods of time. At 75mph I'm right around 2150 and it's perfect for me.

IMO 4.88's and especially 5.13's on anything under a 35" tires, is just too high of rpms. I guess if you're at 5k+ elevation and run a lot of mountains where the speed limit is 55-60...but down here 70mph is slow on the highway, and driving down to San Marcos the tollway that detours you around Austin has an 85mph limit.

What’s your gas mileage like??


2018 2500 6.4 4x4 4.10 Amsoil SS 0w-40, Softopper
Black Rhino Armory 18x9 +12mm
Cooper St MAXX LT295/70R18

2016 Durango 5.7 AWD 3.07 Amsoil SS 4 Qts 5W-30 and 3 Qts 0W-40
1996 Nissan Altima 2.4 Amsoil SS 5W-30

 

[RAM_Designs]

What’s your gas mileage like??

12.5-13.5 on the EVIC, majority highway miles driving around 75-80mph.

 

[AFMoulton]

12.5-13.5 on the EVIC, majority highway miles driving around 75-80mph.

Nice! With 37’s that’s pretty good


2018 2500 6.4 4x4 4.10 Amsoil SS 0w-40, Softopper
Black Rhino Armory 18x9 +12mm
Cooper St MAXX LT295/70R18

2016 Durango 5.7 AWD 3.07 Amsoil SS 4 Qts 5W-30 and 3 Qts 0W-40
1996 Nissan Altima 2.4 Amsoil SS 5W-30

 

[Ratket]

If you plan to stay on 34”s- then 4:88”s would likely be a good gear set. Mds will definitely activate more and give you more drive ability but BUT if you tend to speed, say 80mph or faster a lot then prolly look at 456. When I was planning to do gears on my 6.4 the max speed limit was 65 where I lived and 5k feet up to 8500feet, so I was pretty set on 4:88”s and I was only going to run a 34” Tire.

Even with stock tires and 4:10”s unless you got a tail wind the struck can still feel as if it logs in 6th. I don’t think you would be unhappy with 4:88”s, but I think 4:56 would leave you saying “ ya 4:88”s would of been good.

Just my opinion.

 

[RoadRamblerNJ]

Go 5.13’s. @U&A swapped his 3500 6.4 Hemi to 4.88/4.56s(can’t remember which)and has a thread on here somewhere about his experience. This difference between 4.88/4.56 is sooo small it’s almost not worth comparing. I plan to do 4.88’s, because that is the best for the tire I Run and what I want to do.

This truck with 4.10s and heavy tires gets me on avg 15.1 MPGs around town. And roughly 16-18 on the highway.


2018 2500 6.4 4x4 4.10 Amsoil SS 0w-40, Softopper
Black Rhino Armory 18x9 +12mm
Cooper St MAXX LT295/70R18

2016 Durango 5.7 AWD 3.07 Amsoil SS 4 Qts 5W-30 and 3 Qts 0W-40
1996 Nissan Altima 2.4 Amsoil SS 5W-30

+1
I'm driving the same truck and after doing all the math, I will put 5.13s in as soon as the $$$ fairy arrives.
There is no cheaper way to multiply torque on these trucks. Go big or go home.

 

[olyelr]

Yes, I have searched and read all the forum threads, and have played with the calculators plenty. I guess the question that I am wanting answered is a question of which RPM is the engine going to run most efficiently. Will it be more efficient at 1900 RPM, or 2100 RPM? Is the difference negligible? Will the MDS kicking in at 2100 actually be more efficient than if it kicks in below 1900? These are the questions that bear asking in my mind. I am less concerned with performance (as either one will be a huge upgrade) as I am trying to squeeze out ever MPG I can out of this honking behemoth of a vehicle.

Call me crazy, but those are my concerns.

You’re crazy.

 

[SuperBeeMike]

I regeared my truck to 4:56's about a year ago. I cruise the highway at 2,000 RPM's at 70 mph. I typically see 16/17 mpg on the highway and 13/14 in town (summer gas and calculated via the dash). In the winter I lose about 1mpg. Towing my trailer, I see 7/8 mpg depending on load and headwinds. I don't exceed 65mph with the RV trailer. I do drive like a gentleman. One thing to note as well, my MDS does not come on anymore then it did before. MDS is pretty much un-useful and only activates when my truck is slowing down.The biggest thing to consider is when using tow/haul mode with a geared truck, the computer locks out 6th gear. In tow/haul mode at 65mph (5th gear), I'm turning 2500 RPM's which is just right for my RV towing needs. I really don't want to go any faster with my RV trailer. But when I'm towing the flatbed with a car on it, I can't use tow/haul because I like to go faster and it will push the rev's further than I like. Something else to think about.

Now that I have over 15,000 miles on my 4:56's, I have no regrets and would not go any lower. Below is a quote from my initial post regarding my gear swap.

Hello everyone, this is my first reply here, I just signed up. I have been stalking this Forum for quite some time, and mainly the posts regarding gear changes.

When I bought my truck new, I looked all over for a 4:10 geared truck, but had no luck. I found the perfect truck, but with 3:73's, so I figured I'd give it a shot. It drove fine and pulled ok on flat ground, but it needed more. I was mostly convinced I needed gears after months of reading forums, but ultimately decided after a camping trip to the Ichthyosaurs State Park, in Nevada. My toy hauler is a 33' bumper pull, weighs in around 10k when loaded, and my truck is detailed below. On that trip, I was pulling a grade up out of Gabbs Nevada, had a decent run at it, and was letting the Hemi eat. Halfway up I was down into 1st gear, it was miserable. I tried to push it to second but once it shifted, it bogged and I was right back into 1st. I ended up slowing down so the engine was at 4k RPM's for the remainder of the grade. My wife had that disappointed look on her face, and I'm sure I did too. My mighty Ram was not so mighty. Worse was it ate through my gas which did not give me enough to pull the trailer back to civilization. I had to unhook the next day and take a day trip to Austin for fuel. That worked out, because we took back roads, which led us to a sweet little creek to fish.

So enough with the story, I pulled the trigger two weeks ago and had my truck re-geared. I went with AAM 4:56's for my stock tire, stock height truck to replace my 3:73. I had Driveline and Gear Service, in Sparks, Nevada, do the work for me. They use factory AAM parts and did have to replace the front carrier assembly to accept the 4:56's. It took them 2 days to complete the job and it cost just over $2700. No whine, no funny noises, and a 12 month warranty. I recommend them if you are close. http://www.drivelineandgear.com/

My thoughts are Ram should be building these trucks with 4:56 axle ratios. They might have their reasons on why not too, but it drives like I think it should. I know I have a large displacement Hemi with a good amount of torque now. Its quick, well mannered, and a blast to drive. My gas mileage went up on my daily commute which is mostly city driving. I am currently just under 14mpgs in the city, based on the dash readout, when before I barely broke 13. When on the highway, I notice the MPG reading to be high teens, but I haven't driven far enough on the highway to give you decent data. Running 70 mph on the highway, in 6th gear, my RPM is at 2000. One thing I expected to see more was ECO mode but it still isn't on as much as I'd like. Pulling the trailer now is far less stressful. I don't have to ring the Hemi's neck in 1st to make up for the ridiculous gap between 2nd gear. That extra leverage the 4:56's give really get things motivated now. I have yet to pull a big grade at speed but should be heading out later today for a trip.

I want to stress this to those that are thinking about re-gearing, or are planning to purchase a Hemi truck. It will never be a Cummins powered truck, no matter what we do to them. I have had 3 Cummins trucks over the years and my Hemi will never pull like them. With that being said, I am glad I made the switch to a Hemi and don't think I will ever go back. Daily life with my 15' Ram 3500 with the Cummins was terrible. It had horrible drivability and too many issues that came with the complex emission systems. Another thing to consider is the price of gears and are they worth it to you. I pull my trailer a lot, in Nevada which has the most mountain ranges in the US, 150 of them I think, and I swear I'm always pulling into a head wind (Utah sucks and California blows). For me, they are absolutely worth it, I would have paid more. I also love the new driving characteristics. It is more responsive and quite fun to drive. I hope this helps you in your decision and good luck....Mopar or No Car!!!