M1028 4.56 to 3.73 ?

[98G]

Just had a thought, I do want to eliminate the clutch based limited slips


So blazer with th400, 3.08 gears can cram 20mpg.
I dont see why I couldnt at least match that with the overdrive and closer gears in a m1008. Especially since a blazer with th400 doesnt have lockup, so theres some parasitic loss at cruise and acceleration.

I think I remember people commenting on the 6.2 being able to pull the truck down the road at sub-2000rpm range upwards of 65mph. Although probably not very efficiently. But still the engine seems to have plenty of torque to be efficient at, say, 55mph.
I plan to drive pretty lazily. After all, driving habits are the biggest factor in MPG.

As to your jeep example, I don't think a gasser is a great example of what mpg is possible in a truck like platform. A friend of mine has a ram 2500 cummins and manual and gets 25 mpg at 55mph. Of course it has all the torque it needs to push it down the road and up mountain passes in OD, but push it over 65mph and suddenly it can drop below 10mpg. And those trucks I believe have 3.73 with option for 4.10. To match their torque, they also weigh a lot more than a m1008, but pretty similar aero.

I had a 2004 Ram 2500 with 5.9 Cummins and auto transmission. 3.73 gears. Stock tires. 21mpg generally and never less than 16mpg. I never really towed heavy with it.

I currently have a 2008 ram 3500 with 6.7 Cummins and G56 6spd manual transmission. 4.10 gears. 34" tires and a couple inches of lift. 18mpg cruising empty. As low as 12mpg towing a gooseneck at 36k.

The above isn't really relevant to the 6.2. Modern common rail compared to mid 80s tech.

I had an M1009. Got 20ish mpg out of it.

I get 14mpg out of my M998. KS to GA and back. Towing a welder dropped that to 12ish.

I still think you won't do much better than a stock M1009 for mpg with the 6.2.

I'm not sure why we're focused on mpg anyway. If mpg is the goal, these aren't the means....

 

[erasedhammer]

I had a 2004 Ram 2500 with 5.9 Cummins and auto transmission. 3.73 gears. Stock tires. 21mpg generally and never less than 16mpg. I never really towed heavy with it.

I currently have a 2008 ram 3500 with 6.7 Cummins and G56 6spd manual transmission. 4.10 gears. 34" tires and a couple inches of lift. 18mpg cruising empty. As low as 12mpg towing a gooseneck at 36k.

The above isn't really relevant to the 6.2. Modern common rail compared to mid 80s tech.

I had an M1009. Got 20ish mpg out of it.

I get 14mpg out of my M998. KS to GA and back. Towing a welder dropped that to 12ish.

I still think you won't do much better than a stock M1009 for mpg with the 6.2.

I'm not sure why we're focused on mpg anyway. If mpg is the goal, these aren't the means....

Found a few posts on thedieselpage about some people getting 20+ with nv4500 and 3.73/4.10.

One thing I did not mention is I do want to change to a non clutch limited slip diff. Something around the truetrac design, which would require replacing the carrier unit anyways.

If 3.73s are too tall for highway speeds, 4.10s are also an option, and seem pretty popular. But I keep hearing 1800-2200 is sweet spot for mileage, so might as well gear it so freeway speeds lie perfectly within it. Ideally putting the 6.2 at 1800 at 60ish mph, which I think 4.10s could do with 33s.

 

[cucvmule]

Less torque is needed with higher numerical gears to have a better mechanical advantage.

Transmission gearing is a compromise of having the best gear speed for optimum advantage of the available torque.

I would say that if you ask any trucker what is the biggest factor in driveability he will say gearing vs torque or horsepower.

They are all compromises.

 

[shotty]

4.10s with OD would get you close to the same engine speed as 3.08 without OD like the m1009. 2000 RPM for 65mph.



Even with 4.56 gears you're only looking at 2200rpm for 65 mph in OD.

 

[Recovry4x4]

My truck has changed a few times, next should really tell. Started out stock then had SM465 manual with 4.56 gears. It was okay. Next went to 4.10 gears. Here in the mountains, I gave up hills with 4.10s but getting used to it. Truck is in the garage waiting on me to install the 4500.

FYI it's a dualed out contact truck that pushes 8000# with tools on board. Mileage? Never considered that.

 

[erasedhammer]

Now that I've driven it around with the nv4500 and 4.56 I'd say 4.10s would be perfect.
I can't stay in 5th for any hill right now anyways, so dropping to 4.10s isn't going to make a difference, except in flat cruising.

 

[Recovry4x4]

I know this thread has been going for a while and I've not been around. I have read all the posts and I may duplicate something but I'd like to post this for future reference. EH, is your truck and M1028A2 or M1028A3? I'm assuming its a dually since your referring to the Dana70HD. Carrier breaks for the 60 and 70 are between 4.10 and 4.56. Now, if you had a 4.10 or higher carrier, they make a thicker gear in say 4.56 that would bolt up or one could us a ring gear spacer. I don't think they make thinner ring gears.

When I installed 4.10 gears in my truck, I did it reluctantly. A friend bought a cab & chassis truck just so he could get the axles from it. He approached me looking to convert the front to single wheel. After much thought, I ended up swapping my 4.56 single wheel stuff for his 4.10 geared c&c stuff. The C & C uses a narrow 14 bolt dually rear so all I had to do was remove the Detroit No-Spin from the carrier of the original 14 Bolt and put it in the C & C axle. Both front 60s were open so no loss there.

After your observation of driving with the NV4500 and 4.56 gears and still downshifting, maybe I'll be okay with my 4.10 gears.

 

[shotty]

Some math I did when looking into the nv4500 swap for my truck showed me that swapping to 3.73's will get you an overall ratio in second gear that is essentially the same as first gear in the th400 with 4.56's. This means second is like the old automatic first gear, and you still have the granny first when needed.

Then again these trucks are power limited and don't do great at speed in overdrive so maybe 3.73 + OD would be close to useless? It would let you cruise at 65-75 from 1800-2000 RPM though. With an eventual 6.5 swap in the future maybe it will work out well. I don't have a lot of hills around me to test with.

I plan on following the same plan you are. Did the NV4500 swap, see how it is. Snag a 6.5 and then decide on gears if it has enough power in 5th.

 

[Keith_J]

It takes the same horsepower to move the vehicle at a set road speed regardless of engine RPM. This engine is most efficient between 1800 and 2400 RPM. At 3600 RPM, fuel consumption is 13% greater, due to volumetric efficiency loss and greater heat loss to the pre combustion chamber cooling jackets.
At 2400 RPM and wide open throttle, the engine is generating 135 HP, consuming 8 gallons per hour. That is about 7 miles per gallon at 50 MPH in stock form. Typical unloaded fuel consumption is 16 MPG so it takes 60-65 HP to scoot the vehicle.

So if you drop to 1600 RPM at that speed, you are going to be at the floor of the peak efficiency any lower and torque loss will be noticable. Remember, peak efficiency and peak torque are the same engine speed range.

 

[combat jump]

I swapped my stock M1028 gears to 3.73. Had 4WheelParts do it, actually. total cost was around $2,400, I think (about 7 years ago). It made the truck drive-able on the freeway with no lift. I did loose the locker up front in the process, but could have added one that fit... for the cost of a new locker. It would ad a lot of cost, so skipped. To do over, I would just go with bigger tires and a lift; it would be much cheaper, and keep the front locker.

 

[Recovry4x4]

This is interesting. I really thought I screwed up switching from 4.56 to 4.10 now that the NV4500 is going in. Looking at your post and considering the 1800-2400 powerband, mine might be perfect. Using the Grimm Jeeper gear calc online, here are some of the numbers for my combo (235/85R16 tires).
MPH; 55=1791, 60=1954, 65=2117, 70=2279, 75=2442 and 80=2605. Interestingly, using the same calculator shows that with my SM465 (direct drive 4th) I would only be going 60 at 2605 RPM. I have no intention of going 80 but 75 downhill to make it up the next hill before it drops to 50 is possible.
Thanks for making me think.

It takes the same horsepower to move the vehicle at a set road speed regardless of engine RPM. This engine is most efficient between 1800 and 2400 RPM. At 3600 RPM, fuel consumption is 13% greater, due to volumetric efficiency loss and greater heat loss to the pre combustion chamber cooling jackets.
At 2400 RPM and wide open throttle, the engine is generating 135 HP, consuming 8 gallons per hour. That is about 7 miles per gallon at 50 MPH in stock form. Typical unloaded fuel consumption is 16 MPG so it takes 60-65 HP to scoot the vehicle.

So if you drop to 1600 RPM at that speed, you are going to be at the floor of the peak efficiency any lower and torque loss will be noticable. Remember, peak efficiency and peak torque are the same engine speed range.