If you chose the 4.7L over the 5.7L for fuel economey alone you made a HUGE mistake.... the 5.7L actualy gets the same and is some cases BETTER MPG than the 4.7L..... The reason is the 5.7L makes MORE low end torque than the 4.7L.... when your trying to move 6,000+ lb's from a dead stop the 5.7L will do the task with less effort (fuel) than the 4.7L....

SO yes this all applies to the 4.7L & 5.7L in the 3rd Gen Rams.

Speed Safe, AIR RAM

 

AIR RAM, no i got the 5.7L Hemi :P So I'm off to a better start to begin with? But still, the upgrade to 4.56s, I'm going to still see great improvements? That is awesome! And also, do you know about having to replace the front Differential Gear? I have 3.93s in there now.

<update> Just found out you will have to replace both differentials. Front and back (according to other people) on the 4x4 model. And lets hope better gas milage! What kind of gas milage did you get BEFORE the switch AIR? And what kind did you get after? Both City & Highway? If you have those numbers.

 

Wow I'm extremly interested in this upgrade. I thought I was doing well with 3.92's (better gears than most trucks around here). However I'm not satisfied with the 13/14 mpg I get. I've been wanting better since I got the truck. What kind of actual MPG increase can I expect? Also where could I get this done and how much would this installed run? I have a 4x4, 4.7.

 

Justin:

I would guess you could call up your local dealership's part's department. I am going to make a few calls today after work and find out how much for the set (Front & Back) and see if they say anything about gas mileage.

I will try posting price for both and see what kind of installation costs they throw at me if I buy the kit from them or from someone else. My dad knows a guy that is a parts manager that usually (so he tells me) gets part's cheaper. I will see! If you find anything out, please post :P

-- K

 

Stop thinking about differential ratios,
and start thinking about overall gearing including the effects of tires sizes.

Figure out for yourself the MPH per 1000 rpms.
For best MPG on the highway you need to be around 40 MPH per 1000 rpm.

Notice that is just a little higher than what
Dodge sets the factory stock 5.7 Hemi/545 trans/drivetrain at.
(80 MPH at 2100 rpm)
That is no accident.

Can a vehicle have a 4.533 differential
or even a 4.765 dif
and still get good MPG at highway cruise?

Yes - if the top gears, tires and engine crank stroke combinations are set right

See these articles:
http://makeashorterlink.com/?Z10521C9C
and
http://makeashorterlink.com/?M31512C9C

Keep in mind that engines with short strokes can run a bit more rpm than engine with longer strokes.

To get good MPG you want to keep friction low inside the engine
at the same time that you get high cylinder pressures
and then expand those pressures as much as possible on the power stroke.
This generally means as low an rpm
with the throttle blades as open as you can get without going into
the PCM computer's 'Power Enrichment' mode where economy is thrown out the window.

Here the 4.7 is different from the 5.7 or 3.7 V6 - and this is one of the reasons GM's 5.3V8 does as well as it does.

Will changing to 4.56 differential gears help 0-60 acceleration?
Yes.
Will changing to 4.56 differential gears help quarter mile ET?
Yes, but generally less than people guess.
Will changing to 4.56 differential gears help highway cruise MPG?
No. (unless you change out the Overdrive planetary in the trans to match)
Will changing to 4.56 differential gears help city MPG?
Won't matter much - what trully matters is if you have a heavy foot.

What do all these posts about 3.55 vs 3.92 vs 4.10 vs 4.56
differential gears indicate?

They indicate that Dodge
has not put good durable transmissions
with enough gear ratios
to give both optimum acceleration
and to give optimum highway MPG.

Dodge pickups owners are blinding themselves concentrating on little tree branches
and not stepping back and seeing the forest.

 

So, switching over with my configuration I have now, to a 4.56, I wont gain anything really around town, and will loose it after 40ish mph? And that is where I'll be most of the time once I move a bit south and actually be on an expressway to get to work. So this obviously isn't worth it for the better gas milage.

The only thing is i'll be happier with the quicker accerlation times :P Which more or less is pointless to me because I'll end up loosing the gas milage issue. *sigh*@#!$

Would I loose any gas milage do you think? Could be worth it. I will be towing soon enough as well :/ So a 4.56 will help me out a bit there too. I know I will prob bet more gas milage hauling a 7000lb trailer... but what about without it? If I wont loose anything, and be happier with a 'peppier' truck and save gas when hauling a trailer, then still possibly a good decision to go with a 4.56?

-- K

 

I don't think some of you are getting it. There is no magic gear ratio for better everything. You will gain and lose by going to taller gears. If you tow/haul alot, go to larger and heavier tires and/or wheels or want to drag race a 1/4 mile, you need taller gears. There will not be an improvement in fuel mileage for just normal day to day driving and in fact you will probably lose mileage under those conditions. There are a lot of factors that play into swapping gears that can help or hurt you but the biggest is driving habbits. I suggest using Google.......

 

Actually Hank I have found BEST fuel economy to be at or about 2,000-2,500 RPM’s @ 60-65MPH give or take. And more than a few HEMI owners have reported the same. For best all round performance you should aim to have your RPM’s to be close to 2,000RPMs@60-65MPH.

The formula needed is:

Trans gear x rear gear = overall gear ratio

SPEED x OVERALL GEAR RATIO x 336 / Tire height= RPM

But again RPMS have LITTEL to do with actual fuel economy... yes RPM’s do affect fuel economy but not nearly as much as engine load. Lower the load on the engine and you will increase its efficiency.







So I guess the poor fuel economey is no accident either.....? Dodge has these trucks geared WRONG so if its NO accident then its a real bad joke.





Hank you address things we have little control over. We can not go into our engines and change the stroke; we can’t change the transmission to be geared better... so we are left with what we can do. Now I agree we can complain about the poor fuel economy and suggest they add one of these transmissions you speak so highly about but until then... again the only option we have is a gear swap.






Hank your FLAT wrong here. You’re talking with NO experience to back it up. Sure you read a few books that lead you to your OPINION but you lack the actual real world experience... there for you should take a back seat and leave the suggestions to those who are INFORMED with real world experience.






I agree with you here Hank... so with all your wisdom what is your suggestion to improve fuel economy???? If you read this last statement your "Indications� suggest a "enough gear ratios" that gives "acceleration
And to give optimum highway MPG".... Hmmm that’s funny... That’s EXACTLY what you get when you install 4.56's!

Isn’t it the OVERALL ratios that matter...? Why are you so bent on transmission gearing when in fact you have ZERO control over that gearing... and you can get the same effects with rear gears? ALSO one point that you FAIL to realize is by moving the MECHANICAL advantage to the rear end you take the stress away from the transmission and move it to the rear end... But this super transmission would have to be built to withstand MUCH more load to move the High gears you’re so bent on owning. Again you have NO control over your transmission, but you do have control over your rear end!






So gears are the "little branches" and the "forest" is the transmission... please helps me out here... You suggest that we should change the gearing in the transmission instead of changing the gear ratio in the rear end....???? I’m sorry Hank but a 3.05 rear gear is a GREAT gear to have on the highway... always has been.... I'm not sure why all of a sudden it’s a bad gear to have and that it has become OVERNIGHT a gas guzzling ratio.

Hank, Perhaps you do not feel 4.56's can increase fuel economy because you have not PHISICALY witnessed the gains first hand. So I can honestly understand why you say NO 4.56's will not help fuel economy. BUT the Facts are Facts and this FACT has been proven by more than a few people 4.7L owneres and 5.7L owneres alike. You only gain 300 RPM’s at 60MPH going from a 3.55 to a 4.56. The 300 RPM gain reduces the load of the engine at that RPM, the fuel economy gained by the lower engine load is greater than ANY negatives to the 300 RPM gained.

I do agree that your right foot is one of the biggest factors in fuel economy but my point is that with 4.56's you can literally have your cake and eat it too. And if dodge did add a lower gear to the trans we would get the same results... but the problem is WE CANT change our transmission gearing and the wishing Dodge had done it does not fix what we have. So rear gears are the ONLY way we can get the mechanical advantage to help move our 6000lb truck from a stop and maintain speed pushing through the wind on the highway. So in a way what you are saying backs up the rear gearing you just WISH Dodge had geared the transmission better... but again we can’t fix that... but we can still get that mechanical advantage foe better efficiency.

Until you have actually DONE this mod (4.56's on a 3rd Gen Ram specific) and witnessed first hand the PRO's & CON's you are just SPECULATING and your theory lacks REAL WORLD testing to back that theory. I have done the math, which at first I was a bit nervous on what the outcome would be... because it was a theory at that point.... then I spent my money because I knew MATH had only one right answer.... and it all looked good paper. So I took the next step and put my money where my mouth was... And NEVER looked back!

SPEED SAFE, AIR RAM

 

NO this is not the case... Hank has been trying to push his theory for years now... He is wrong, he has NO real world experience and speaks his OPINION rather than FACTS. Sometimes he post some good (Long CUT & PASTE responces) but here he is FLAT wrong.

If you went to a 4.56 rear gear you would get BETTER fuel economey up to 65-70MPH... at 75-80 it will be about the same as your seing now... after 80 it starts to go downhill. You need to look at the 4.56's as a 3.05 rear gear... because thats EXACTLY what you get with your .67 overdirve. A 3.05 gear is a highway gear. When your NOT in overdrive then you have the 4.56 ratio... and that helps lower RPM towing and increases fuel economey in the city due to having better mechanical advantage moving you off the line from a dead stop.

NOW under a heavy foot YOU WILL SEE A LOSS in fuel economey... but the fun factor will be twice the fun. The 4.56's under a light foot will increase MPG.

Ask around.... head over to Dodge Talk or Dodge Truck world and ask ANYONE who has installed 4.56's..... they (in most cases) will tell you the same thing I have been saying.

SPEED SAFE, AIR RAM

 

Please read all the FACTs that have been posted, with a 4.56 you GAIN an overall gear ratio of 3.05... 3.05 has NEVER EVER EVER been a bad gear to have for highway driving.... its the OVERALL gear ratio that has EVERYTHING to do with fuel economey. When choosing an OVERALL gear ratio you need to take into consideration TIRE hight & vehicle weight .... Notice I say OVERALL gear ratio and NOT rear gear ratio... It does not matter if you improve your 3.05 ratio from going to a lower gear in the rear end or a higher gear in the trans... the OVERALL ratio is whats moving the vehicle. The difference is when the overall ratio is improved with the transmission gearing you INCREASE the stress in the transmission.... but when you improve the overall gear ratio in the rear end you move that stress to the rear end and remove it from the transmission.... SO this brings up a NEW POINT..... the 4.56's in the rear end will LOWER the stress on your transmission, it will LOWER the heat in your transmission and increase the life of your transmission....

This is NOT an opinion.... this is a PROVEN FACT!

SPEED SAFE, AIR RAM