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2nd Gen Non-Engine/Transmission changing gear ratio for better mileage

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2nd Gen Non-Engine/Transmission Front Wheel Bearings 95 3500

Engine/Transmission (1998.5 - 2002) amsoil 15w40HDD vs 15w40 CJ4

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Has anyone ever changed an auto 4x4 from 4. 10 to a higher gear ratio. If so how did it affect your fuel mileage. I am curently cruising at 2200rpm on the highway and would like to get down to 1700-1800 instead but only if it will gain mileage without killing my towing to bad
 
In theory, changing to 3. 54 gears will increase your fuel economy slightly but in the real world, particularly with a 47RE with loose converter, the results will probably not vary much. Even if you save a mpg or two it will take many years for the tiny increase in fuel mileage to provide a savings after you consider the cost of parts and labor to change it out.
 
If you tow with it or run large tires like 35s you are going to make the trans work harder. And the truck will feal lazy.



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93 250 2wd xc auto 354 273k

04. 5 3500 4wd qc dully 373 6speed 100k
 
I currently have 3. 54 gears and 35" tires. I can't wait to change to 4. 10 or 4. 30 (37s in the future). I would keep your 4. 10s, or swap axles w/ me :D
 
2200 RPM on the highway isn't going to hardly hurt MPG, especially if you've bumped your timing up to say 16-17 degrees. With timing advanced around there the ideal RPM should be about 2000 which isn't far from 2200. With advanced timing and big tires most likely you'd lose MPG going to 3. 54s
 
I was not thinking of going all the way down to 3. 54's I have 4. 56 gears now and figure with my 35's it would be equivelant to stock tires with 4. 10's. My timing is already at 16. 5 degrees. I was thinking of going down to a 4. 10. I have tried everything else I can think of to get better mileage but nothing has worked. I only get 12. 5mpg on the highway empty and I am grasping at straws at this point
 
Are you sure you have 4. 56 gears? That ratio was not offered in the Dana rear ends used in Gen II trucks w/Cummins engines. I think it was offered in gas powered 4x4 Rams.
 
I averege 16 mpg city/highway, 17 highway, 20 on a slow country road doing 45-50 mph. I lug the engine a lot around town. I try to keep the OD off until I get on the highway. I am not very happy with my current gearing. I think I would get better milage with a lower gear (higher numerically). My dream setup would be 4. 56 gears with a gear venders OD unit. Lockers of course. Sounds like your half way there. If you swap do a Dana 80, you con have 4. 30 gears. For some reason I cannot find anyone that manufactures 4. 30 gears for the Dana 70.



I like the US Gear approach to an overdrive better than the gear venders. US Gear opperates more like a manual transmission and the GV opperates more like an auto. US Gear has been sold and the new owners have chosen to not continue manufacturing the OD. Unfortunate.
 
Are you sure you have 4. 56 gears? That ratio was not offered in the Dana rear ends used in Gen II trucks w/Cummins engines. I think it was offered in gas powered 4x4 Rams.

Yes, I have a detroit locker in the rear and the gears were changed. I run 2265 rpm at 75mph which by calculation shows me that is a 4. 56



I averege 16 mpg city/highway, 17 highway, 20 on a slow country road doing 45-50 mph. I lug the engine a lot around town. I try to keep the OD off until I get on the highway. I am not very happy with my current gearing. I think I would get better milage with a lower gear (higher numerically).



I have the 4. 56 gears and I am turning 2265rpm at 75 and can't use OD under 60mph without it getting hot. I have been told 17-1900rpm is the best range for mileage. A 3. 73 would be 1874rpm in 3rd at 55mph and 1764rpm in OD at 75mph. If you are looking for mileage I would stay away from the 4. 56 am only getting 12mpg highway
 
Mine has the 3:54's and ALWAYS gets around 19 mpg, no more... no less. 33" tires and I typically run between 67-75 mph, I believe it's turning something like 1800-1900 rpm. I don't recall it going as low as 1700? When I kick off the OD it bumps it up tp 2200-2300. One thing that is very noticable is the noise! the truck is much louder at 2200rpm!... and all that extra noise makes for more road fatique. I run the truck about 600-700 miles per week, and that's several 3+ hour drives. To me the truck is really comfortable to travel in, I don't tow anything of any size and I like the 3:54's.



Personally I have always believed the 3:73's are the perfect truck gears.
 
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must be your big tires keeping rpms down because i am turning about that rpm with 4. 10s, i only get 12 when towing something non aerodynamic though, i have never put a hwy tank through it where i wasn't towing something so i don't know what my hwy mpg is, i have been getting 14. 5-15 on my combined with my foot to the floor with the only mpg consideration being keeping hwy cruise 70 or less, been thinking hard about loosing the flatbed and dumbo ears towing mirrors for a stretched dually bed (stretched to fit my frame, my best guess is my C&C runs a short cab on a extra cab length frame) seen a couple in pictures and they look cool, enough room for stacks a tool box and still have a 8" box :-laf save some weight and look better but the flatbed is so damn handy/forklift proof



Yes, I have a detroit locker in the rear and the gears were changed. I run 2265 rpm at 75mph which by calculation shows me that is a 4. 56







I have the 4. 56 gears and I am turning 2265rpm at 75 and can't use OD under 60mph without it getting hot. I have been told 17-1900rpm is the best range for mileage. A 3. 73 would be 1874rpm in 3rd at 55mph and 1764rpm in OD at 75mph. If you are looking for mileage I would stay away from the 4. 56 am only getting 12mpg highway
 
Yes, I have a detroit locker in the rear and the gears were changed. I run 2265 rpm at 75mph which by calculation shows me that is a 4. 56

I have the 4. 56 gears and I am turning 2265rpm at 75 and can't use OD under 60mph without it getting hot. I have been told 17-1900rpm is the best range for mileage. A 3. 73 would be 1874rpm in 3rd at 55mph and 1764rpm in OD at 75mph. If you are looking for mileage I would stay away from the 4. 56 am only getting 12mpg highway

1700-1900 is ideal RPM for timing that's closer to stock, 1700 is definitely too low of RPM for pushing big tires and/or going 75mph. . . should be at 1900 minimum.

The challenge with P-pump engines is the narrow "ideal" RPM band thanks to the fixed timing. The BSFC charts tell the tale, you can see comparing the charts that the p-pump 12-valve engine burns more fuel per HP when below or above the optimal band by 200 or so RPM. That's compared to any 24-valve engine through at least 2006 as well as VE 12-valves.

My 2003 got slightly worse MPG than either of my 12-valve rigs empty. When towing my smallish travel trailer at mid-upper 60s on the highway both 12-valve trucks get 13-14. 5 MPG. My '03 pulling the same trailer at the same speed normally delivered 15. 5-17 MPG. I figure this was mainly due to frequently running the trans in Direct vs OD to avoid lugging the engine and the HPCR engine uses less fuel at ~2300 RPM.
 
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3. 54 gears were great when I had stock or even 33" tires. When I put 35s on, It destroyed my performance until I made power upgrades. I'm still way out of my power band. The power upgrades were really just a bandaid for the real problem of gearing. I cannot even consider my plans of 37" tires until I address the gears. I don't tow as heavy as I did in the past, but a good FOR SALE sign on the side of the road could change that any time. lol
 
vaughn, is it posible to move the sweet spot to 2200 rpm or is it stuck at 1900. I just ran to california at a steady rpm of just shy of 1900 today and my mileage still seems to be the same as before (about 12) but I have not filled the tank yet. I grossed out at about #13,500
 
just filled up after mom drove my truck for nearly the whole tank and discovered what its capable of mileage wise with the 4. 10s 20. 4 mpg or about 5 more then it gets when i drive it, i think she drove a good mix with town being on the strong side of the combination, id never guessed it could get that good a mileage, guess my foot is that heavy, part of the problem is i don't drive it as much as i use to and have too much fun hauling azz every time i get into it
 
me too actually, i even asked her if she added any fuel and the answer was no, kinda makes me a little happy in the fact that if the truck can get that it must be healthy :-laf



I can drive mine like miss daisy or like don garlits and it still gets the same
 
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