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Discussion Starter · #1 · (Edited)
O.K. here it is....., This is for all you guys with 4.10's & 4.56's that state that your highway mileage at 65-70 MPH is about the same as the rest of us that have stock 3.55 & 3.92 gears.

There's no way to prove that you "geared guys" get better city mileage..., but enough of you "geared guys" have stated this as fact. So let's take it for a fact that you'll get a 1-3 MPG increase in city driving below 45MPH. That's a MAJOR plus to getting these gears already..

Next, lets focus on the highway mileage....., this is where I have a problem. Some of the "geared guys" have posted that their highway mileage is about as good as with stock gears below 65MPH. I have to believe that once you "geared guys" are traveling at 65 MPH and above, your mileage will suffer greatly.

Simple experiment.

I have an '02 quad cab with auto tranny (45RFE with a .75 to 1 gear). The tires are Goodyear Wrangler 20's which are 33" tall. The rear end is geared with 3.55's.

These are the comps:

1600 RPM's @ 60MPH = 23-24 MPG (as registered with the overhead computer).

1900 RPM's @ 70 MPH = 21-22 MPG (as registered with the overhead computer).

2100 RPM's @ 80 MPH = 18-19 MPG (as registered with the overhead computer).


All of these reading were taken in "clean" air - don't drive behind a car or truck because your mileage will increase - and on level ground. The windows were up AND the A/C on. I set the cruise control at the mentioned speed and let it stablize over a mile or so.

If enough of the "geared guys" post their results it should FINALLY clear up the gear debate.., Thanks in advance.
 

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It will only be the same if the tires and rims are the same size. Most of the "geared" guys here ( I am about to join them) have bigger meat to turn. That is a big reason they go to the 4.10 and 4.56's. So for you to disprove them...you would have to have 2 truck of the same build with the gears being the only diffrence. But I will have to agree with you. I have yet to understand why everyone is saying that they are getting better mpg...
 

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Discussion Starter · #3 ·
I agree...., the 4x4 guys are pretty much out of the running with the example that I posted above. There are alot of guys that are running the taller gears on their street rides (4x2). AIR RAM, Reorg, etc.... If we can get them to post, that info will also relate to the 4x4 crowd. Not exactly, as you stated, but in general.
 

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How did you get 20s with the 3.55

I thought you had to get 3.92 to get the 20s

Or did you add them later
 

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My truck doesnt have enough power to go on the freeway in overdrive after i lifted it and put her on 35's with the stock rear end 3.73's. Therefore i am running at 2700 rpms at 70 mph with overdrive off with OD on i run about 1800 at 70 mph. I've got the 5.9 with K&N FIPK2 intake and fowmaster 40 muffler. get about 13mpg highway in OD and about 14-15 mpg with OD turned off. Can't wait untill i get put my 4.56's in!
 

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Jquint,

You can check and see what it would be like to have 4.73 diff gears instead of 3.55

You can do this simply by pushing your 'tow-haul' or overdrive button to turn off your topmost gear and drop back into 1:1 3rd gear.

1 to 1 ratio with 3.55 diff gears is the same as 0.75 ratio with 4.73

I think you will find that your highway MPG will be worse.
Try it and see.

I know of
NO DRIVETRAIN ENGINEER AT GM, Ford, OR DAIMLERCHRYSLER
that will tell you that you will get better MPG,
either in the city or on the highway,
with 3.92 or 4.56 gears instead of your 3.55 diff gears.

I do know several engineers who will tell you that if you switch to 3.21 gears you will get about 0.5 to 1 MPG better on the highway in the 55-75 mph range, but that your acceleration will be less in all gears.

I also know that Mercedes is switching all their automatic transmissions to 7 speeds so that they can have high numerical ratios in gears 1-2-3 for acceleration, and low numerical ratio overdrives in gears 5-6-7 for good fuel economy on the highway.
 

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HankL, that's not precisely true

if Air Ram and them say they're turning approx. 2200 rpms with 4.56's

with OD off you'll be turning 3200rpms

OD doesn't drop down to third, or a 1:1 drive in our trucks, it's kicks out the 5th OD, and drops back to 4th, which is about .85:1 or so I believe

also, with 4.56's you won't see 3krpms+ unless you're running an auto tranny with no overdrive in it

my 68 Torino GT with a third gear 1:1 drive and 4.11's turns 2800 rpms at 65, my Dodge 3.73's with overdrive off and 38's turns 2100 rpms at 60
 

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On my 97 I had 33's. I went from 3.55 to 4.10. My gas mileage was much better. With the deeper gears my motor didn't have to work at all to get me going 60mph
 

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Discussion Starter · #10 · (Edited)
We've crunched all these numbers previously...., there is no concrete rear gear vs. OD on..., vs. OD off...., that we can apply. All things change when your at speed and factor in all of the variables. Wind resistance, (friction), speed, (MPH), tranny gearing, etc....., For instance, AIR RAM & Reorg posted that they are doing 1900 RPMs at 60 MPH..., I'm doing 1600 RPM's @ 60 MPH, not much difference. BUT, Reorg recently posted that he's doing 2550 RPM's at 80 MPH while I,m doing 95MPH @ 2550 RPM's. That's a BIG difference in speed.

My, so called "experiment", will give the street guys a good idea in what to expect when you go from one extreme - 3.55's with street tires - to the other extreme - 4.10's or 4.56's with street tires-. on level open highway with the OD/ON and the cruise control/ON and the windows/UP and the AC/ON etc....., We won't get the same numbers if you've got a 4x4 or if you have a 5-45 tranny'd truck or a 3.92 geared truck, or a HEMI'd truck, etc..., but we'll get a good idea where we're at with the MPG's on the highway for a 3rd GEN RAM..

I really do believe that these "geared guys" get better MPG in the city...., I'd just like to see how much - if any -worse their mileage is on the open highway. Thanks.
 

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HankL said:
Jquint,

You can check and see what it would be like to have 4.73 diff gears instead of 3.55

You can do this simply by pushing your 'tow-haul' or overdrive button to turn off your topmost gear and drop back into 1:1 3rd gear.

1 to 1 ratio with 3.55 diff gears is the same as 0.75 ratio with 4.73

I think you will find that your highway MPG will be worse.
Try it and see.

I know of
NO DRIVETRAIN ENGINEER AT GM, Ford, OR DAIMLERCHRYSLER
that will tell you that you will get better MPG,
either in the city or on the highway,
with 3.92 or 4.56 gears instead of your 3.55 diff gears.

I do know several engineers who will tell you that if you switch to 3.21 gears you will get about 0.5 to 1 MPG better on the highway in the 55-75 mph range, but that your acceleration will be less in all gears.

I also know that Mercedes is switching all their automatic transmissions to 7 speeds so that they can have high numerical ratios in gears 1-2-3 for acceleration, and low numerical ratio overdrives in gears 5-6-7 for good fuel economy on the highway.

Seems hard to believe that with all the emphasis on CAFE that they wouldn't be putting 410 or 456s in as standards/options if they gave better gas mileage

Unless it is because the people in the federal bureau automically associate
them with poor mileage and Dodge GM or Ford don't want to fight them

Why else put out trucks with rears geared to poorer mileage such as 3.21 3.55
if they truely do

Whole issue is baffling
 

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Discussion Starter · #12 ·
I can easily see where these trucks will get better city mileage with the tall gears. AIR RAM has made a very good argument documenting the same. My main interest is seeing what the MPG numbers are on the open highway...., I know he was talking about getting 20MPG at 60 MPH but I don't know about you guys...., I never do 60 MPH on the open road. More like 70 to 80 +...,
 

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Well guys, I drive a 95 4x2 1500 xcab, and all I can say is when I added my 4.56 gears (previously had 3.55) and no tire change (265/70/17) my mileage increased in town from 10.5 to 11.5, and on the highway it went from 16 to 17.5. This was with a 5.9 with just a few mods. I know that the numbers don't and won't crunch with a calculator, but the 5.9 runs more efficient on the highway at around 2200 to 2500 rpms. Every engine has it's own particular sweet spot for mileage. I know my wifes 4.7 Durnago 4x4 gets 22mpg on the road and about 14 in town. So in conclusion; I can't say that gears will help the 4.7 in mileage. But if you are getting what your computer says (usually they're generous) I wouldn't complain anyway. Now that I have done major modding to my truck the milage is even better.
 

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My 04' Hemi Quad 4x4 came with the 3.92 gears and 275/17 tires. I lifted it and put 315 BFG tires on it. The larger diameter tire dropped my overall rpm's and forced the truck to work harder to get it and keep it rolling. The change also brought the truck out of "specs" for the stock shifting patterns and power bands that DC engineers intended. The new tire size made the 3.92 gears act and drive like 3.42 gears.

The 4.56 gears I had installed, combined with the new 315 tire diameter, brought the truck performance closer to the original ratios DC engineers designed the truck to run at. The 4.56's with the new tires brought the actual ratio to about 4.15's. A little higher than factory intentions, but with added tire weight/rolling resistance/towing demands, the ratio works fine.

The gearing around town gets me rolling easier and quicker. Hills and passing on the freeway take less engine effort.

It is what it is. If I hammer it on the freeway and keep it above 75mph, my freeway mpg suffers about 1-1.5mpg. My stats and figures come from a GPS, and not the cheesy on-board computer. I've also had my speedo flashed for the new tire size, and it's pretty close to GPS.

A 2-wheel drive doesn't have the extra weight, rolling resistance, and other 4x4 issues, so a 3.73 or 3.42 should work fine with a hemi.
 

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As request by JT....at least once a month I drive from Lubbock to DFW (or vise versa). When I had only 4.10 gears, I would get around 16-17mpg. When I added the electric cutout, PowerWire, AIRRAM CAI, and JetStreat those numbers went up into the low 20s. The most I have ever recorded was 24mpg. My speeds usually average 75-85, depending on what city I am in.
 

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I'm one of the 4.10 gear guys...

I'm running a 2005 Ram 2500 QC LWB (only ~150# difference between LWB & SWB), Hemi, 5 speed automatic, stock 4.10 stock gears & 265/70/17 tires. According to the overhead computer, I'm averaging 10.7 mph in the city.

Now, for all you frothing at the mouth for 4.10 or 4.56s, I can speak about the 4.10s. When ya romp on 'er, you do have lots of get up 'n go. HOWEVER, 99% of my driving doesn't entail such an aggessive driving style.

Here's what I hate about my 4.10 gears (and I suspect 4.56s aren't much different):

Speed limits around here are between 35-45; and it's grows old real fast to feel the truck continually shift between 4th (~1900 rpms) & 5th (~1300 rpms) in traffic when doing speeds between 37 & 43 mph. It's continual - back and forth between the gears while driving in traffic. I highly suspect if I had 4.56 gears, I'd experience the same issue with lower speeds, say 35-40 (guestimated). I wonder if the 3.92 gear crowd is experiencing this with their 5 speed automatics.

One thing tho: I wish Chrysler would have geared the trans differently so that 5th didn't kick in until 60 mph OR created a 6th gear for that speed range.

That's my two cents.
 

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DamnYankee

drive around a day with OD off and see if it helps, you should stay right around 1900 rpms (maybe 2100) and not shift into 5th
 

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I tried OD off city driving: mpg drops below 10 on the overhead computer.

Now to preface this, I have no axe to grind and I'm not whining about the gas mileage - I bought this truck because its high performance engine (plus, I've been a long time mopar driver for decades).

After reading alot of posts in here, I think I must have a one-of-a-kind 4.10 geared Hemi Ram. My MPG numbers don't come close to what some in here posted they get with their 4.10/4.56 gears. And I know I don't benefit gas mileage-wise from a higher revving engine (OD off) during city driving. I certainly don't get 20 MPG highway as others have claimed - it's more like 15-16 mpg - and that's riding on puny 265/70/17s. You can bet MPG will drop if I switched to 315s.

I'm not trying to piss on anyone's parade, I'm just giving you some real numbers from my truck which is completely stock. So for those of you considering 4.10 gears or lower (eg, 4.56), give it some careful thought before you jump in and raid your differentials.
 

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Discussion Starter · #19 · (Edited)
DamnYankee said:
I'm running a 2005 Ram 2500 QC LWB (only ~150# difference between LWB & SWB), Hemi, 5 speed automatic, stock 4.10 stock gears & 265/70/17 tires. According to the overhead computer, I'm averaging 10.7 mph in the city.
Can't compare your 2500 with the 1500. Although your truck carries the same engine & tranny....., the rear end of the 2500 is a 10.5" not a 9.25". Also, the curb weight of your truck, assuming it's a 4x2/QC is about 5776 LBS vs. the 1500 4x2/QC which is 5015 LBS. Don't know of any other differences.
 

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I will go for a ride tonight and get some numbers for you guys... Remember RPM's do not go hand and hand with fuel economey, Higher RPM's does not always mean more fuel. Your engine has a sweet spot where it will run most efficient. My tires are as SHORT as they come as well and my best fuel economey comes at 60-65MPH... when I had my 20's my best fuel economey came in at 65-70MPH. Also remember I have the 45-RFE with the .75 OD and with the 4.56's I have the equivelent of a 3.42 rear gear... you guys with the 545RFE will have a 3.05 ratio which will allow you to get better fuel economey at 70+MPH. ...

As for shifting in and out of gear... you should have your rear checked! Once im going 35MPH in OVERDRIVE there is NO hill on this planet that will cause my transmission to downshift... It stays put unless I put in that OD gear untill I my foot to the floor. So if your transmission is searching for gears... you need MORE gear!

I will take a spin and post some more numbers for you guys...

SPEED SAFE, AIR RAM
 
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