Do you have a lot of stop and go or is it slow speed cruising? A tighter converter would help a lot. I believe the stall speed on a stock converter was 1800 rpm? If you don't need the flatbed getting a regular bed would help too by reducing weight.

Here is what Ive done to my 93 to help mpg

2nd gen 4"dp to a 3rd gen 4" exhaust. The 3rd gen exhaust has smoother smaller bends than the 2nd gen system had.

Bhaf, straight aluminum tube to the turbo, 56mm wheel housing.

16cm exhaust housing.

Coolertubz intake horn, grid heater delete. Believe it or not these two things dropped my egt's by 100f and gained some power.

Stock injectors, power screw turned in 3/4 turn, smoke screw turned out to reduce smoke on acceleration.

No tailgate seems to help too. I don't know if its that I dumped 50lbs or if it affects airflow.

I try to keep the pyro at 400-450 cruising and the boost no more than 3psi. yes my pyrometer is accurate .

Mixed city/hwy I average 20.5 empty constantly. Long trips empty I average 25 if I keep it at 62 mph, any faster and its 19-21. I did average 27mpg on one trip but I think outside temp (110-117) was a big factor. I have never been able to get that high again. I'm tempted to try a partial belly pan just to see if it does anything.

 

X2 on the nice pics.
What/how does the timing bump help mileage?

 

Heres what I posted on another site about the same question, couldn't figure out what was killing his MPGs...

Start with whats expected, here is what you get right from Cummins:

Q: What is the typical fuel economy of a Ram with the Cummins diesel?

No such thing as typical! Loads, right foot "operation", frontal area, terrain, temperatures, and winds vary widely!

Here are some 12V rules of thumb: Due to EPA emissions regulations, ISB engines get 2 mpg less than the 12 valve engines.

3/4 ton 2WD with manual, street tires and
3.54 axle: 23 empty, 20 loaded, 12 -17 mpg towing
4.10 axle: 21 empty, 19 loaded, 12 -16 mpg towing

3/4 ton 2WD with automatic, street tires and
3.07 axle and 3 speed auto: 20 empty, 18 loaded, 12 -16 mpg towing
3.54 axle: 21 empty, 19 loaded, 12 -16 mpg towing
4.10 axle: 20 empty, 18 loaded, 12 - 16 mpg towing

3/4 ton 4WD with manual, trail tires and
3.54 axle: 22 empty, 19 loaded, 12 -16 mpg towing
4.10 axle: 20 empty, 18 loaded, 12-16 mpg towing

3/4 ton 4WD with automatic, trail tires and
3.54 axle: 21 empty, 18 loaded, 12 -16 mpg towing
4.10 axle: 20 empty, 18 loaded, 12-15 mpg towing

ALL 4WD trucks:
Larger tires do not hurt mileage and may actually help by 1/2 mpg. (Note: not wider)

Lift will cost about 1 mpg for each 2", brush guards and winch bumpers will cost 1 mpg

1 ton 2WD, 4WD - look at comparable 3/4 ton and:
take 1 mpg from empty and loaded mileage, towing mileage is about the same as 3/4 ton

All models: expect 1 - 2 mpg less in winter

Did you put on new tires? Bigger/wider tires will kill mileage, taller and skinny are better. What is your PSI? They will also throw off your speedo making your mileage off, does it match a GPS? Odd but true, are your tires aligned? (rolling friction)

Here is an article on a 1997 Dodge Ram 3500 Dualie Cummins - Diesel Power Magazine the truck is getting 30MPG

Do your tires/gearing keep you in the Cummins "Sweet Spot" 1300-1500 RPM Cummins Turbo Diesel News and http://cumminsengines.com/assets/pdf...whitepaper.pdf Its for the big trucks but the principles are the same. It shows oil/fluid type, air temp, idle time, speeds over 55 and a host of others all eat away at mileage.

Fuel: summer fuel gets 3% better mileage than winter. Winter air can drop mileage by 8-15%. Warming up the truck in the mornings 1/2 a gallon an hour at 650 rpm, do that for 10-15 minutes, 5 days a week.... B20 can lower your mileage by 1%.

Not to be funny but do your boots need to be dropped off to the local cobbler and have the lead removed? Cummins claims a 30% difference in MPG between a good driver and a bad one.

Hope it helps.

 

A question on the "sweet spot" thing. My truck has an nv4500 trans and the original 12v. I am content to run 1400 - 1500 RPMs in 4th on rural roads, but I just don't feel good lugging the engine that low in OD. I instead run the engine at close to 1650 RPMs : the point in the RPM range with the lowest BSFC. Is there a way to tune the truck so that 1450 RPMs won't sound like it is hammering the gear off the shaft?

To the OP: The best MPG bump I got was adjusting the timing up a bit. It increases cylinder pressure, making each bit of fuel put more work into the pistons and less heat into the exhaust manifold. Hamilton cams also makes a fine product that is known for increasing mileage. I believe the cams will work in your engine.

 

Camshaft

 

Ran down to my brothers for a Hamilton Cams seminar, then a New Years party, then back home.

I ran 2300-2500 rpms down and back for 250 miles. About 75-80mph. By looking at this tank, looks like 16mpg and added some oil to the crankcase. Guessing my lift pump went out. I am waiting for it to completely cool before I know for sure.

Sent from my rooted Velocity Ally

 

Best (consistent) mileage I ever got was 24 on a stone dead stock 1991 5 speed intercooled dually ,with stock 215-85-R16 tires and no wind.
It also had 4.10 gears.

I strongly do NOT recommend 3.07 gears if you plan to tow any appreciable weight without a 6 speed.

Mark.

 

hey-Hey!!!,
I have 3.07 gears and an NV5600 trans. I went from Philly to Ann Arbor on 25 gallons( 600 miles )with a fair bit of stuff in the bed( a gen set/welder and a hot air balloon ). AC on the whole way. Speed 65-70, mostly close to 70 mph.

Warm up in the winter cuts mileage, as does letting it sit and idle ~5 mins when it is cold out.
cheers,
Douglas

 

I got 26 mpg once.I did everything I knew to get the most I could get,1993 d250 3;54s ,518 AT,extended cab.from southcarolina to georgia all flat land,80 psi in e rated tires,fairly warm day,a/c off,windows up,all interstate ,drafting when I could,cruise locked on 65 mph.this was before the 2nd gen intercooler and the 4" exhaust,which didn't seem to help the mpg.
I get an average of 21 mpg don't seem to matter how I drive.I removed the heater grid but didn't help either.

 

diesel fuel burns at a given rate which correlates to piston speed. That said, Cummins engines will get their best efficiency between 1600-and 1900 rpm. With a 6.7l that number goes down a bit due to faster piston speed, but then you have more friction from the ring and piston.

Cams will definitely help peak the efficiency of any engine if you have a cam that does two things.

1. allow more air to be trapped into the combustion chamber at the speed at which you drive, which allows a higher peak cylinder pressure. A higher peak cylinder pressure allows a better expansion ratio.

2. allow more energy to be spent on the piston without losing too much spoolup.

By the way, unloaded my 1999 2500 regular cab with a 3.07 rear end gets just under 26mpg cruising at 69mph @ 1780 rpm.

 

How did you get a 3.07 under that truck? Dana 70U?

 

3:07's are in the Dana 71 axel, they came in our trucks with some packages.

 

I got right at 19mpg @ 70-75 mph running across the state of MI once with whats in my Sig. This truck stock averaged 17-20 mpg Also i pull a toy trailer that weighs 11,400 empty & it pulls good with this gear ratio I have been through quite a few states with this setup & i like it do to the fact of the trued & tried 727 3 speed I have a 518 2wd trans & the rest of the drive line to bolt right into this truck. But i don't think that will happen

 

Zach has a 89 or 90 automatic rear in it.

Sent from my rooted Velocity Ally

 

I'm thining of swapping in a Dana 70 with 3.07's. Any thoughts if this would be too high a diff ratio for my CTD/NV4500 set-up?

Obviously I'd have to swap back to a 3.54 for pulling a trailer.