N.Johnson

Here's a thought. The 305/555 2003-04 seem to be getting better mileage than the 325/600 or 610. With the 305/555 maximum torque according to the specs is produced at 1400 rpm. With the 325/600 or 610 max. torque is at 1600 rpm. Could this account for the mpg difference?

RAMRODD

I know the 1 gen ram had manual hubs for 4x4, Not sure about the system on the 2 gen rams. But I know the 3rd gen rams the front axil shafts for the 4x4 turn all the time and are just engauged at the transfer case this has to rob a lot of HP and lower your mpg by at least 1. Couldn't this be part of the reason why the 3rd gen mpg are less then the older trucks.

johnr9q

I thot my 99 had a "straight thru" lock up overdrive?

johnr9q

When I bought my 99 I didn't push getting a manual transmission cause I was assured that the automatic with overdrive would lock up in 4th gear and be just as effecient as a manuel in high gear. Are some of you saying that is not true?

Raspy

The idea that the auto has an overdrive and is not straight thru, as well as having to maintain oil pressure all the time, makes it less efficient than a straight through design. Of course the six speed has an overdrive too so it's not perfect either. I don't think an auto can ever be as efficient as a manual because of the torque converter (when not locked) and the oil pressure requirement. The old three and four speed trannys, in high gear, were just conected straight through with no gears carrying a load. It's too bad the new six speeds aren't straight thru in 6th with a little higher axle ratio of about 2.61. That would be the same overall gearing as a 3.73 rear end with a .70 overdrive and would eliminate running the power thru an extra set of gears in 6th.

Wetspirit

sled4fun

That is correct Johnr9q. Overdrive when locked up is more efficient that overdrive without lockup, but whenever you use a overdrive gear it is just one more gear set that needs to be turning and this lowers efficiency. It would be better to have the final cruising speed ratio determined by the rear end gear set with input speed set at the sweet spot of the engine output speed. Then adjust transmission gears to accordingly. Of course as you raise your diff. ratio to say a 3.23 you will loose low end power when towing.

This is why a 6 speed manual with a granny low if needed for a heavy load would be best if 6th gear was 1:1 output and the diff. gear setup for max. engine sweet spot rpm when crusing.

If automatics were set up this way it would also be better, but i think they are more interested in the using the word "overdrive" and using existing parts tooling etc. to keep costs down.

All in all I think they will all start having more interest in MPG in the future rather that HP wars just because we are demanding it.

I also think that dissengaging the front axles from our 4x4 trucks would be a good start in helping MPG numbers.

Mark Hodowanec

Another advantage to this would be that the axle ratios would be numerically lower. Axle gears that are numerically lower have less sliding or the hypoid, and thus are more efficient. In other words, for the same degree of power transmitted, and the same wheel speed, a 3.73 will be more efficient than a 4.11. So there would be two advantages to eliminating the overdrive - strait thru gearing on the tranny & numerically lower axle ratois - both would help the efficiency!

sled4fun

Another good point Mark.

Remember the old two speed powerglide transmissions from GM. First gear would get you to 60+ mph. If I remember correctly a lot of saturday night stock car racers used to use this transmission because it was very efficient in transfering HP for an automatic. Of course 2nd gear was a straight through 1:1.

xmr

When I bought my '99 it got 19 to 20 in city driving and 22 to 25 highway. Unfortunatley I found that it had the #53 block and it was cracked. Rather than repairing it ( the crack appeared to be too long) I replaced with another engine that had about 40,000 less miles. It gets 17 to 18 city and 21 to 22 highway. I then bought a smarty. on s/w 1 my highway mileage dropped to 20.5 and I get 18 to 18.5 city. I tried s/w 7 and got 16.7 city and did not try to get a highway mileage figure ( sure did like the way it ran it was awsome). I am trying to find time to redo my hydrogen/oxygen generator and see what it will do. I know that tree dr. has had good results with his unit. I also plan on checking and cleaning my iat and map sensors and adjusting my valves and then see if any of that helps.

6cylinders

There is a gentleman on another forum who has a F350 duallie, he has been experimenting with mods for MPG.
He got some good results from lowering the truck. I think that was his biggest gain. It was good reading I wish I would have book marked it.

chuxtruk

The only thing I would add is that by reducing drag the mileage goes up...so reduce some drag and either take off your tailgate and replace it with one of those cargo nets or at the least, open it and place it in the down position. I've heard improvement ranges just from that alone of up to 5% on long distance freeway runs.
I would also run an additive in the fuel or run a B-20 mixture of biodiesel....my mileage has improved from the past use of each. On this tank of B-20 I'm getting 23.2 which is up from the 21.2 I normally get running straight #2. And keep your air & fuel filters up to snuff. We all know what happens with clogged filters.
Also when possible, if you're interested in the best mileage your truck could get, use your cruise control. It'll do a better job of saving fuel than your trust in your right foot, that's for sure. Especially on those freeway runs.

sled4fun

It has been proven and said over and over that maximum mileage will be had with the tailgate in the UP position as opposed to the down position, use of net etc. I believe that a flat top cover over the bed rails gets you the best mileage of all. Was this a myth buster test also?

J&L

lot of factors in mpg between the Cummins engines such as 3500 DRW/auto.4.10/4x4/big tires/stuff we carry/heavy add on front bumpers/city driving/etc. These add up to poor milage. Compare that to my 2500/QC/3.73/NV5600/stock tires/2x4 and the most important item is my 110 + mile a day hiway commute. I've drove this for 35+ years and can write a book on things tried for better mpgs, gas or diesel. The current '03 305/555 engine will average 22+ mpgs tank after tank for 55000 miles on this commute. On long trips it has ran a few 23.7-24.2 tanks at highway speeds. My previous '01/2500 235/460 auto/3.54 ran a consistant 19.5-20 mpgs on the same 110 mile a day commute for 65000 miles. All pencil figures. It would be interesting if Cummins gave some insight why the 305/555 engine/NV5600 puts down some very good mpgs.
I've had and wore out 11 pickups in all those years and running oversize tires was one thing that didn't work for better mpgs, gas or diesel. Aired up stock tires, but not wearing the centers, worked the best.
I think city type driving is the biggest hit on good mpgs even on the Cummins.

JIM

big jimmy

I lost 1.5 -2mpg going to bigger tires. I was on a job that had a long downhill grade that I had driven with both sets and with the new tires I could not coast as far by about 1/3rd the distance. It was that obvious.

I do not think these trucks would be so fun to drive if they were tuned to get 26mpg. I have driven box trucks and the like tuned for mpg under city conditions and for all the good things about those motors, excitment, or even calm satisfaction, were not a part of the equation.

I second everything said about air resistance. If these trucks were off the ground 3 inches with an even lower air dam and tiny mirrors and such we would all see much better mpg. I'm not being sarcastic, but I need my truck to be configured like a typical truck, not a saturday night strip cruiser.

Big Jimmy

displacedtexan

You said it well. For many of us, for our truck to do what we need (and sometimes want) them to do, we comprimise. I will sacrifice MPG for the power to tow at the powerlevel I find comfortable, to have the ground clearence and traction I need in fields and muddy jobsites. With my add ons that increase drag and weight...

It is a comprimise. The fact that we get 15 is amazing my gasser NEVER got that. I get similar milage to my Dakota...