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Cummins 5.9 liter and 6.7 liter inline six-cylinder diesel engines

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Cummins 5.9 liter and 6.7 liter inline six-cylinder diesel engines

Section on 1989 adoption of Cummins engines in Dodge Rams © 2008 Curtis Redgap
Thanks to Harvey Barlow for updates/corrections. Updated 6/22/2015.

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The long, happy partnership between Cummins and Dodge actually began long before the 1989 Dodge Ram pickup (Chrysler's first pickup with a Cummins diesel engine.) Indeed, it's possible the two companies would never have hooked up if not for Chrysler Europe - in particular, the former Commer/Karrier company, now owned by Chrysler and renamed to Dodge.

In 1959, Dodge started working on a new commercial truck; the company felt it had to use its own diesel to sell it, and it turned out that only Cummins would license their design for sale under the Chrysler name (full story).

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Back in the USA, Dodge tried using Mitsubishi diesels in light-duty pickups during the 1970s, but they never caught on. Trying again with the big Cummins diesel was a risk, but it definitely paid off.

Part of the reason was that the huge diesel was completely different in character from the little Mitsubishi; designed for tractors, road graders, and such, the turbocharged Cummins "B" engine had entered production in late 1984. It was a relatively simple in-line design, with two valves per cylinder. Not long after production started (in 1985), engineers began adapting the 359 cid, or 5.9 liter, diesel for Dodge pickup trucks. It finally launched in Dodge Rams in 1989, rated at 160 horsepower and 400 lb.-ft. of peak torque.

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The Cummins "B" engine had a 4.02 inch bore and a long 4.72 inch stroke to increase low-end torque. It had 17:1 compression, using an iron block with a steel crankshaft, assembled camshaft, forged I-beam connecting rods, and an aluminum intake manifold. The average first-overhaul time was nearly 300,000 miles, better than the Chevy and Ford V8 diesels by a good margin.

Engines for Dodge were built at the Consolidated Diesel Company in North Carolina; it was originally a joint venture of Cummins and J.I. Case, but Cummins later bought Case's share, so Consolidated Diesel is now the Cummins Rocky Mount Engine Plant. It has 1,900 employees, and exports engines to China (thanks, Walt Mercer). The plant was spotlighted by Fast Company some years ago.

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The B was built with 18 wheelers in mind. Dodge had to make the truck work around the engine.

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Dodge made an outstanding decision in choosing Cummins. Using an inline six, not a V-8, cut maintenance costs; it had about 40% fewer working parts than competitive engines. By the time Dodge put a pickup around it, its record was outstanding.

The long stroke of the 6 made serious torque, far more than the V-8s from GM (246 lb-ft) or Ford (345) at 400 lb-ft. It generated 160 hp at 2,500 rpm.

The engine was direct injected (fuel is squirted into the combustion chamber), unlike the two rival engines, so it threw off less heat, allowing a smaller radiator and less coolant.

Dodge engineered the truck to handle the expected longevity and power of the Cummins. Load carrying was 4,000 pounds above that of its rivals, right out of the box. A Dodge would cost about an extra of $2,043 to be equipped with the Cummins diesel. A good deal, and not overly done, but done just right. Dodge quickly saw sales jump for Cummins-equipped trucks.

The 1991 updates

In 1991, just two years after launch, several changes were made to Dodge Ram pickups with the Cummins diesel:

  • The vacuum pump switched from dual-diaphragm to a vane type
  • Two 750 amp batteries replaced the single 1,025 amp battery
  • A new engine controller, SBEC II, was added; it controlled the intake manifold heater, wait-to-start timer, water-in-fuel sensing system, cruise, and transmission overdrive shift (on trucks with automatic transmissions)
  • Midyear, an air-to-air intercooler was added to cut NOx emissions
  • Midyear, the A518 four-speed automatic was used with the intercooled diesel, in Rams with a conventional cab

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The redline was 3,000 rpm from 1994 through to 1998; the midyear-1998 24-valve engine raised the redline to 3,200 rpm, though by 2000 it was back to 3,000 again.

1989160 @ 2,500[email protected],700 12 valves
1994 175 @2,500420 @1,600 [email protected],500400 @ 1,750
1996215 bhp @ 2,600440 @ 1,600180 @ 2,600420 @ 1,600
Mid-1998 - 2000235 @ 2,700
460 @ 1,600215* @ 2,700420*@ 1,60024 valves
2001245 hp @ 2,700505235 hp460 lb-ft
2002 305 @ 2,900555 @ 1,400
2003-04 CA Std235460235460HP-CR**
2003-04 Standard250 @ 2,700
460 lb-ft250 @ 2,700 460 lb-ft HP-CR**
2003-04 HO305 hp 555 lb-ft305 hp 555 lb-ftHP-CR**
2004.5 325600325600Model 600
2005-07 standard325610325610Model 610
2007.5-2010 (exc below)350610350650
2007-2010 Cab/Chassis 305610
2010-12 Pickups350***610 350800
2013-15 Pickups350**660 370-385800-865
2016 Pickups up to 900

* Automatic and five-speed manual, in 1998; automatic in 2000. ** High pressure common rail *** 305 in chassis cabs

The end result, in 1991, was a truck with 16,000 pounds of gross cargo capacity. That number would rise as time went on; and Dodge would continue to have the most powerful diesel engines in the industry for decades, thanks to Cummins.

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These massive engines helped Dodge by creating a niche market for its pickups, by then over two decades old and not especially popular - Chrysler had a seven percent market share, and half of those were diesels! Within two years, the 100,000th Ram Cummins diesel truck rumbled off the line at Dodge City.

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Changes for the 1994 Dodge Ram

Changes in emissions rules, requiring 60% fewer particulates per brake horsepower-hour (due to the discovery that the particulates raised the odds of getting cancer), the Cummins turbodiesel needed numerous changes for 1994. This included a new fuel injection system and its first catalytic converter. The latter removed about 30% of smoke particulates.

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An in-line high pressure fuel injection pump replaced the rotary pump; the higher pressure atomized the fuel into finer droplets, which burned more completely and also reduced particulate emissions. Individual plungers for each injector were operated by a camshaft through roller followers, with both cam and followers being oil-lubricated.

Injection timing and amount were controlled by the throttle position, which was modified by a centrifugal governor moving a gear rack in the high pressure pump. The rack rotated sleeves with variable width slots that were concentric with the pump plungers. When the engine was shut off, the slot closed completely by an electric solenoid on the outside of the pump.

1994 Ram engines5.9 V8Cummins- StickCummins- Auto
Cubic inches360359359
Horsepower 230 bhp @ 4000 175 bhp @ 2500 160 bhp @2500
Torque330 [email protected] 3200 420 [email protected] 1600 400 [email protected] 1750
Redline5250 rpm 3000 rpm 3000 rpm
Battery (std)600 (750 opt)Dual 750Dual 750

The fuel pump limit on wide-open throttle idle speed was raised from 2875 to 3000 rpm for driveability, and the high speed fuel cut-off was made more gradual as well. Dodge claimed the new pump was also more reliable.

A second, piston-operated lift pump assisted and helped to cool the high pressure pump, providing fuel to the high pressure pump at 211 bs/in2 and making sure that the high speed pump was always full (the engine already had dual pumps, but the new pump was higher capacity). An external priming plunger aided in restarting after running out of fuel.

An improved fuel filter between the two pumps and a larger water separator was needed for the higher fuel flow rate; a new 100-micron strainer between the gas tank and fuel lift pump removed more particules. A fuel heater prevented waxing in cold weather. A water drain and electronic water sensor were carried over from prior models. The fuel filter was replaced every 12,000 miles; oil, every 6,000 miles.


Throttle response and low speed torque were increased by adding a waste gate to the turbocharger, and by using a smaller turbine wheel and nozzle which reached peak boost more quickly. The waste gate opened at high engine speeds to protect the turbocharger. High altitude performance was unaffected by the waste gate.

The compressor had "Map Width Enhancement," which recirculated a small amount of air back into the compressor at the mid point of the blades, thinning the boundary layer of air on their surface; this increased flow and pressure at high speed.

The Cummins turbodiesel kept its eminence among diesel pickup truck engines in fuel economy, beating the 1993 Dodge Ram diesel pickups; though it was aided by a lockup torque converter (on automatics), better aerodynamics, and lower rolling-resistance tires. The engine was now too powerful for the automatic transmission, so Dodge artificially restricted power on trucks with automatics.

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Larger diameter, straighter ducting from the turbocharger to the charge air cooler and from the charge air cooler to the intake manifold reduced air flow restrictions. The intake manifold elbow was cast aluminum and the ducts were rolled aluminized steel.

A larger charge air cooler (often called an intercooler), which spanned the width of the radiator, reduced airflow restriction for greater power and lowered charge air temperature to reduce NOx emissions.

The intake manifold air heater, which aided low temperature starting and reduced white exhaust smoke, had a more efficient heating element. A new control schedule shut off heat when vehicle speed exceeded 10 mph.

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A narrowed piston-ring land above the top ring, and a revised combustion chamber "bowl" in the piston crown, lowered emissions. A new combination of ring materials and construction cut oil use.

A larger diameter crankshaft vibration damper was used on engines with manual transmission to compensate for increased torsional vibration from higher power.

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Engine warm-up was speeded by separating the thermostat and "jiggle pin," sealing the thermostat at low temperature and putting a separate jiggle pin unit into the cylinder head. The jiggle pin lets air trapped in the coolant escape from the block and head when the engine is cool, but seals when the engine is running for faster warm-up.

The automatic transmission adapter was lengthened so a torque converter clutch could be added.

The air cleaner included an air flow restriction gauge called the Filter Minder™ to clarify replacement times, since air filters on diesel engines cut performance and economy more quickly than on gasoline engines, but elements which look dirty but are not plugged protect the engine better than new ones.

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The Filter Minder worked by measuring air pressure drop on the "clean" side of the filter, with a check valve holdng them at the highest restriction that the filter had experienced. When the ring reached a red zone on the scale, the filter needed to be changed. Pressing a button on the top of the housing reset the Filter Minder to zero.

A silver cast-aluminum appearance cover with red Cummins Turbo-Diesel logo concealed the six individual steel valve covers for improved appearance.


In 1996, the Cummins diesel was rated at up to 215 bhp at 2,600 rpm and 440 lb-ft @ 1,600 rpm, with a 3,000 rpm redline. In 1997, the throttle control system was refined and hydraulic power brake booster was added.

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In midyear 1998, a 24-valve head replaced the old 12-valve unit, and a new electronically controlled fuel injection system replaced the mechanical system. For Rams with the manual transmissions, 20 hp and 20 lb-ft of torque was added; with automatic transmissions, horsepower increased by 35 hp. Fuel economy increased nearly 5%, while maintenance intervals were extended to 15,000 miles for fuel filter changes, and to 7,500 miles for oil filter changes.

The 24-valve heads increased airflow and allowed vertical injector mounting over the center of the piston bowl for improved combustion, low-end torque, and responsiveness. A Bosch VP44 electronic fuel pump with higher injection pressures and electronic controlled timing helped responsiveness over the entire power range.

Other upgrades included an overhead valve rocker system (150,000 miles without adjustment), a redesigned piston for increased power and efficiency, reduced noise, and cleaner operation. The engine met every 1998 California Air Resource Board (CARB) emissions standard without a catalyst or Exhaust Gas Recirculation (EGR).

There were two versions of the Cummins "B" turbodiesels used in Dodge trucks between 1998½ and 2000 - a 215-horsepower engine that was paired with the 47RE automatic transmission (ending production in December 1999), and a 235-horsepower version that was paired with either the NV4500 five speed or NV5600 six-speed manual.

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For the 2001 model year, buyers could get either a 235 hp engine or a high output 245 hp version, differing mainly in the computer calibration (there were 18 calibrations in all, depending on model year, pollution zone, and truck type).

The 245 hp version was only mated to the NV5600 six-speed manual transmission only, and had a 17:1 compression ratio. Instead of using a crankshaft position sensor, the tone wheel on the crankshaft was moved to the camshaft gear on the front of the cam, and the camshaft position sensor filled both functions. Forged aluminum pistons had a different bowl shape for higher compression, and the powdered-metal valve seats were now inserts. A larger flywheel was used to accommodate the larger splines on the NV5600, and the six speed used a 330-mm clutch rather than the former 310-mm one.

The 24-valve high output's fuel system was also different, though the name was unchanged. The fuel-injection pump had higher pressure and for higher-flow fuel injectors. High output engines had the old turbos, the other engines had a new turbo with fewer parts.

The engine data plate, on the left side of the gear housing, lists the horsepower, serial number, and other information. In the eighth position of the VIN, the 215 and 235 hp versions of the standard engine are coded as 6, and the 245 horsepower version is coded as 7.

2002: new 5.9 liter diesel block and injection

In model-year 2002 (calendar year 2001), the engine was avagin revised. The truck now had a a class-leading trailer towing rating of 23,000 lbs (GCVWR). The new engine delivered 555 lb.-ft. of torque at 1,400 rpm and 305 horsepower at 2,900 rpm.

Nearly 75% of Ram 2500/3500s were sold with the Cummins Turbo Diesel engine option. Now, Cummins had a new block and high-pressure, common rail fuel-injection; the average major overhaul interval was raised to 350,000 miles. Oil drain/filter service intervals were doubled to 15,000 miles for schedule A service and to 7,500 miles for schedule B service.

The common rail fuel systems for the 2003 Dodge Ram Heavy Duty used pilot injection, putting in a small amount of fuel to start combustion before the main fuel charge was injected, to cut noise and improve cold starting (verified as far down as -40° Farenheit).

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An electronically controlled, gear-driven fuel pump provided up to 23,200 psi (1600 Bar) of fuel pressure, and was less dependent on engine speed than traditional systems.

For model year 2003 (introduced in 2002), a higher fuel pressure version was brought out, rated at 300 hp in the high-output/manual transmission model.

Starting in 2004, there were again standard and high output forms - 250 horsepower and 460 lb-ft of torque in the standard output version, and, starting in 2005, 610 lb-ft of torque in the high output version (the Cummins 610). The diesel Ram could tow 23,000 pounds (gross combined weight). The Cummins was the most powerful diesel engine available in its class.

The high-output Cummins 610 used a revised piston combustion bowl; the electronically controlled turbocharger (still using a wastegate) matched boost pressure with engine needs to avoid exhaust gas recirculation, dropping over 50 components. The 610 was presumably named after its torque rating, 610 lb.-ft. (827 N•m) starting at 1,600 rpm.

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Durability was helped by gallery cooled aluminum pistons, Inconel® exhaust valves, high-cobalt Stellite® exhaust valve seats, a high-strength exhaust manifold with multi-layer gasket between head and manifold, and forged steel, fracture-split connecting rods.

The horsepower rating went up to an impressive 250 horsepower at 2,900 rpm (from 235 horsepower at 2,700 rpm) and produced an equally impressive 460 lb.-ft. of torque at 1,400 rpm.

In midyear 2005, the 325 hp / 610 lb-ft version of the engine was brought out; it would last through to the end of model year 2006.

2007: moving to the 6.7 liter form and cleaning up the smoke

Cummins acquired full ownership of Tata Holset Ltd., a joint venture with Tata Group created in 1994. The company was renamed Cummins Turbo Technologies, the group it worked under. Holset branded turbochargers and other products, though, would still be sold to Tata and others (including Cummins India, Eicher Motors, Mahindra & Mahindra, and joint venture Tata Cummins). Cummins had strong growth in India, expanding its facility in Dewas in 2005. Tata Holset had made turbochargers for medium and heavy duty diesel engines used in power generation and vehicles. Over 200 people worked at the plant.

In January 2007, Dodge announced Rams with a new 6.7 liter Cummins turbodiesel that met the EPA's standards for 2010 three years early. Sold with the 68RFE six-speed automatic, the 50-state-clean diesel included an emissions-reduction system originally developed by KonTec, with Cummins' own filters and systems. Dodge claimed a 20%-40% cut in fuel use, and up to 90% cut of oxides of nitrogen, largely due to an adsorber catalyst. Tom LaSorda claimed that the Ram - Cummins "is the cleanest diesel truck available on the market."

Cummins produced the 1.5-millionth diesel engine for the Dodge Ram in 2006. 80% of Dodge heavy duty truck buyers bought the diesel in that year.

A cooled exhaust gas recirculation (EGR) system was re-introduced. The piston combustion bowl was redesigned again. A new turbocharger had variable geometry. Within the exhaust system, a self-cleaning DPF and an oxidation catalyst reduced particulate matter by a factor of 10 and was certified for 120,000 miles.
A new closed crankcase ventilation system ended crankcase fumes and oil carry-over.
Nearly 40% of the new engine's parts were carryovers.

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The Cummins diesel used in heavy duty Dodge pickups and in Dodge chassis cab trucks did use diesel emissions fluid in 2010, and the pickup diesels were given an exemption through 2013 (the chassis cabs required DEF as of 2011).

oh20 had written: "Dodge coupled the new 6.7L diesel engine with a new 68RFE 6-speed auto transmission. The 6.7L Diesel engine option carred a list price of $6,100 ($495 higher than the 5.9L diesel, but exhaust brake included at no charge; models with a standard 6.7 had price hikes of $495.) Dodge also added an "Ultra-Clean Diesel System" charge of $995 for all Rams equipped with the 6.7 diesel engine as a separate line item on the factory sticker [to show where the extra cost came from]."

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When launched in 2009, maximum torque came 400 rpm lower than the GM Duramax, and 100 rpm lower than the Ford Power Stroke (in 2011, all had peak torque at the same 1,600 rpm). The Cummins Turbo Diesel engine also produced 20% more torque at 1000 rpm, and 10% higher clutch engagement torque than its predecessor for better launches and drivability, and fewer shifts.

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Starting in 2007, a single 6.7 liter Cummins diesel was available, producing 350 hp. For more details on the trucks using these engines, including market share and such, see our Dodge Ram 2500/3500 and Dodge Ram 3500 Chassis Cab pages.

The 6.7 continued to use solid tappets (non-roller) to this day, with an adjustment interval of 150,000 miles.


A power boost on diesels for pickups with automatic transmissions raised torque to 800 lb-ft (from 650) and increased horsepower in the normal cruising range by 40 hp. A new torque converter and changes to the shift algorithms help the transmission to handle the load.

An independent 2011 dynanometer test showed the Ford diesel putting out 735 lb-ft, the GM-Isuzu at 765 lb-ft, and the Cummins at the rated 800 lb-ft, all at 1,600 rpm. Horsepower was higher on the Ford and GM-Isuzu.

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There were several calibrations for the diesels, as their unrestricted power seemed to be too much for certain vehicles. The top rating, 385 hp (at 2800 rpm) and 865 lb-ft of torque (at 1700 rpm) was reserved for pickups with the Aisin six-speed automatic. Next came pickups with the 68RFE automatic, at 370 and 800 rpm. Finally, pickups with the manual reached 350 hp and 660 lb-ft. The higher torque of the 865 lb-ft engine came from "more aggressive fuel delivery and turbo boost calibration."

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All 2013
Ram Heavy Duty diesels had a new cooling system, with dual radiators, dual transmission coolers, and a
low-slung charge air cooler to raise heat-rejection capacity by 25%. The Ram Active Air
intake system, triggered by the computer, drew cooler air from the front
of the vehicle when it sensed extreme heat or high altitudes. When conditions were wet, the
system used an under-hood inlet, dry and clear of snow
packing. They also started using urea for a (roughly) 5% increase in gas mileage, according to Cummins.

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The new selective catalytic reduction (SCR) was more efficient than the old
Lean NOx Trap (LNT) technology, and while it required diesel exhaust fluid
(DEF), the Ram had full power when fluid levels were low. DEF is
relatively inexpensive, compared with the fuel savings; easily available;
and does not need to be refilled often. The larger exhaust-gas
recirculation (EGR) cooler slashed soot production and fuel
dilution, allowing best-in-class oil change intervals of up
to 15,000 miles.

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ptschett wrote:

The chassis-cab trucks [not the pickups] had urea, or diesel exhaust fluid (DEF), starting in 2011. The urea system has a way to figure out the quality of the fluid in the tank, so don't just pour in water!

There are some downsides of DEF: it freezes at 12° F (trucks have a heater in the tank, costing some electrical power or robbing some warm coolant from the engine.) It's also corrosive, with a pH of 9.5, wipe those spills up fast!
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Cold-start performance was improved, and a "smart" electronic exhaust brake (using the variable-geometry turbocharger) was added.
The computer had better management of
EGR flow rates and exhaust temperatures to
accommodate de-sooting. [Variable geometry
turbochargers were pioneered with Chrysler's gasoline
engines.] The SCR-equipped diesels were certified to run on B-20
(20% biofuel).

The frame-mounted fuel filter/water separator had
3-micron particulate filtration and water stripping. The unique venting system prevented dirt and
water from entering the tank; a warning light illuminated when the sump required

2016 Model Year Diesel Engine Changes

For 2016 Ram pickups, Cummins provided 900 pound-feet of torque on the Cummins diesel engine for the 2016 2500/3500, setting a record for torque in mass-produced vehicels. The extra torque came from new fuel delivery and turbo boost calibration, and allowed the 2016 Ram 3500 breaks the record, previously held by the old Ram 3500 (at 30,000 pounds) by moving up to 31,210 pounds, more than two tons beyond its closest rival. The 2016 trucks have relatively minor changes to the drivetrain to handle the additional capacity.

Cummins has continued to improve on the original design of the B-engines, keeping them up-to-date workhorses.

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