Anyone ever "de-tuned" a Cummins 5.9 for mileage?

Willl · Apr 1, 2013

24 MPG ?, sweet. Maybe 25 is very possible.

sd455dan · Apr 1, 2013

JerryK said:
My 2002 [old BR body style, 24 valve, 6 speed, 3.54 Dana 80 rear, 4X4 Club Cab] gets around 21 if I keep her around 60mph. Drops off quickly if I try to push her 75, especially if it is windy. I have got as high as 22 every once and awhile. More like 17-18 if I push it.... Empty truck weighs around 7100 pounds. GVW is 8800. But with the sweet sound of the turbo whining, and the Cummins growling down the road.... who cares about fuel mileage...

My 03 6 speed NV5600 3500 HO was used to drive 3000 miles one way trip and then haul a trailer back -hand figured it averaged right at 22 mpg (2003 48 state- no egr,catalytic converter, dpf, urea, but is one of the common rail high pressure injected diesels) Empty , don't have the return with trailer mileage, some say if you listen closely and can keep the turbo slightly spooled but with the throttle at a minimum for the speed you are traveling that and keeping egt down, works pretty good...
With 3.73 and the 6 speed ,the mpg really drops off right around 70mph.. Also anyone tried the new Smarty junior in the de-power mpg mode??

Dmace · Apr 1, 2013

buickanddeere said:
How does detuning an engine boost mileage when the truck still requires 45HP to roll down the highway at 55mph? To overcome aerodynamic drag, rolling friction of the tires, drivetrain friction/windage/pumping losses and acessory loads.

While it may take X amount of HP to keep the truck overcoming all forces against it, it CERTAINLY doesn't need 385 HP to do so. Diesels need fuel to create power so reducing the power (while still obtaining enough to accel the vehicle) will reduce fuel consumption.

There will be a point where there is not enough fuel for such a large displacement engine to be efficient and you'll need to go to a smaller displacement setup but there's definitely room in these diesels to lower fuel consumption and still have a useable powerplant.

Maybe a Multi Displacement System like the gas engines that can shut off 3 injectors in light duty use...

firemanmike69 · Apr 1, 2013

Dmace said:
Maybe a Multi Displacement System like the gas engines that can shut off 3 injectors in light duty use...

With a common rail truck it would be easy and there are already tuners on the market to do just that on class 8 trucks, it seems it would be an easy jump to the medium duty diesel trucks of today

tractorski · Apr 1, 2013

There is a great article in the best of Diesel Power magazine where they took a stock '97 dodge ram 3500 dually CTD and with a little over $9 in changes got almost 31 mpg.

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DT86 · Apr 1, 2013

tractorski said:
There is a great article in the best of Diesel Power magazine where they took a stock '97 dodge ram 3500 dually CTD and with a little over $9 in changes got almost 31 mpg.

Sent from my iPad using TractorByNet

$9? Is that a typo?

firemanmike69 · Apr 1, 2013

DT86 said:
$9? Is that a typo?

Nope they only spend $9.26 on duct tape to get 31 mpg

DT86 · Apr 1, 2013

firemanmike69 said:
Nope they only spend $9.26 on duct tape to get 31 mpg

Gotcha!

JIGBUILDER · Apr 1, 2013

The best of the best Cummins mpgs in a Dodge truck IMO goes to the '03/'04 305/555 HPCR. I had a '01 235/460 Cummins in a 2500 Dodge with a 3.54 axle which ran in the 19.5 to 20 mpg average on the road tank after tank. Because the '01 was noisey enough to kill normal brain cells and wouldn't pull a sick calf on OD I bought a new '03 2500 305/555 3.73 NV5600. Much quieter plus mpgs jumped to 21.5 to 22 average mpg on my 660 miles a week hiway commute. The truck has just over 215k miles and still runs the same mpg average. Best tank mpg was a 23.7 on a 520 mile trip to Fort Campbell, KY in '03 to see my grandson off to Iraq with the 101st. Return trip showed 22.3 mpgs. When the '04.5 came our with the 325/600 engine mpgs dropped as Cummins added a 3rd injection event for less pollution and make the engine even quieter. Check out any of the several Dodge/Cummins forums for more input on the 305/555 engine and great mpgs. All pencil figures.
I tow several GN stock and flatdeck trailers. The truck averages 12 to 12.5 mpg pulling my 11200 lb 5th wheel RV. My wife drives it now as her 5.3 chevy 1500 3.73 axle only gets 17 mpg. Guess who has to drive her gas guzzler now. Yep it sucks ......... gas.

sd455dan · Apr 1, 2013

JIGBUILDER said:
The best of the best Cummins mpgs in a Dodge truck IMO goes to the '03/'04 305/555 HPCR. I had a '01 235/460 Cummins in a 2500 Dodge with a 3.54 axle which ran in the 19.5 to 20 mpg average on the road tank after tank. Because the '01 was noisey enough to kill normal brain cells and wouldn't pull a sick calf on OD I bought a new '03 2500 305/555 3.73 NV5600. Much quieter plus mpgs jumped to 21.5 to 22 average mpg on my 660 miles a week hiway commute. The truck has just over 215k miles and still runs the same mpg average. Best tank mpg was a 23.7 on a 520 mile trip to Fort Campbell, KY in '03 to see my grandson off to Iraq with the 101st. Return trip showed 22.3 mpgs. When the '04.5 came our with the 325/600 engine mpgs dropped as Cummins added a 3rd injection event for less pollution and make the engine even quieter. Check out any of the several Dodge/Cummins forums for more input on the 305/555 engine and great mpgs. All pencil figures.
I tow several GN stock and flatdeck trailers. The truck averages 12 to 12.5 mpg pulling my 11200 lb 5th wheel RV. My wife drives it now as her 5.3 chevy 1500 3.73 axle only gets 17 mpg. Guess who has to drive her gas guzzler now. Yep it sucks ......... gas.

Makes you wonder what a person could wring out of the 305 hp 555tq with the NV5600 in mileage just by replacing the 3.73 gears with the 3.42 ratio that is available with the automatic