Cummins 5.9 liter and 6.7 liter inline six-cylinder diesel engines
At Cummins Engines, a 1989 contract for supplying diesel power to the Dodge Truck Division for its line of Ram pickups resulted, eventually, in a great deal of additional business. General Motors had diesel engines for its pickups since 1978, and Ford since 1983; Dodge was a latecomer, but would end up with the best powerplants of the three.
The Cummins “B” engine, turbocharged like all Cummins applications, was designed for combines, tractors, road graders, loaders, cranes, marine applications, and crawlers. It went into production in late 1984. Work on adapting the engine to pickup trucks began in 1985, with the “B” engine displacing 5.9 liters, with two valves per cylinder; then as now, it was an in-line 6-cylinder turbocharged diesel. When it launched in 1989, it was rated at 160 horsepower and 400 lb.-ft. of peak torque – less than half the numbers for today’s High-Output 6.7-liter Cummins turbo diesel.
The Cummins “B” engine displaced 5.9 litres, or 359 cubic inches. It had a 4.02 inch bore and a long 4.72 inch stroke for gobs of stump-pulling torque, where you need it. The “12 valve” as it was nicknamed had 17:1 compression. It was an all iron block with a steel crankshaft, assembled camshaft, and an aluminum intake manifold. Durability features included forged I-beam connecting rods to bring the average first-overhaul time to nearly 300,000 miles.
The Dodge-destined B engines were originally built at the Consolidated Diesel Company outside of Rocky Mount, North Carolina. The plant, originally a joint venture of Cummins and J.I. Case, now belongs entirely to Cummins, and is called 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.
The B was built just like any other Cummins, with 18 wheelers in mind. There were no shortcuts taken by Cummins, nor any modifications to make it work. The engine was thoroughbred Cummins, period. Dodge had to make the truck work around the engine! (There was already a Mitsubishi diesel powering Dodge D-series trucks, but that engine was physically smaller and produced less torque.)
For Dodge, in 1989, it was an outstanding decision to choose Cummins. First, it was an inline six, not a V-8, reducing maintenance costs. It had about 40% fewer working parts, leading to less expensive and quicker repairs. The engine had been well tested over 5 years before Dodge put a pickup around it, in tougher applications, and its record was outstanding. The long stroke of the 6 made serious amounts of torque, far more than the V-8 rivals from GM or Ford, at 246 ft lbs for GM and 345 for Ford, with the Cummins at 400 ft. lbs. In diesels, torque is king; and 400 lb-ft at 1,700 rpm was hefty. Horsepower was also good — 160 hp at 2,500 rpm.
The engine is also direct injected whereby the fuel is squirted right into the combustion chamber, unlike the two rival engines that put fuel into an indirect injection sequence, with a pre combustion chamber. The result is less heat thrown off from the Cummins, thereby allowing a smaller radiator, meaning less coolant.
Dodge quickly saw sales jump for Cummins equipped diesels. To their credit, Dodge had overengineered the truck to handle the expected longevity of the Cummins. Load carrying was 4,000 pounds above that of its rivals, right out of the box. A suitable 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.
In 1991, several changes were made to Rams 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
Ram diesel pickups had a clutch/ignition interlock, unlike their gasoline counterparts.
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.
|MTX BHP||MTX Torque||ATX BHP||ATX Torque||Notes|
|1989||160 @ 2,500||400@1,700|
|1994||175 @2,500||420 @1,600||160@2,500||400 @ 1,750|
|1996||215 bhp @ 2,600||440 @ 1,600||180 @ 2,600||420 @ 1,600||
|Mid-1998 - 2000||235 @ 2,700
||460 @ 1,600||215* @ 2,700||420*@ 1,600||24V; EFI|
|2001||245 hp @ 2,700||505||235 hp||460 lb-ft|
|2002||305 @ 2,900||555 @ 1,400|
|2003-04 CA Std||235||460||235||460||HP-CR**|
|2003-04 Standard||250 @ 2,700
||460 lb-ft||250 @ 2,700||460 lb-ft||HP-CR**|
|2003-04 HO||305 hp||555 lb-ft||305 hp||555 lb-ft||HP-CR**|
|2005-07 standard||325||610||325||610||Model 600|
|2007.5-2010 (exc below)||350||610||350||650|
* Automatic and five-speed manual, in 1998; automatic in 2000. ** High pressure common rail
The end result was a truck with 16,000 pounds of conservatively estimated 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.
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.
Changes for the 1994 Dodge Ram
Because of changes in emissions rules, demanding 60% fewer particulates per brake horsepower-hour, the Cummins turbodiesel needed numerous changes for 1994, including a new fuel injection system and the first use of a catalytic converter on a Ram diesel. Unlike the catalytic converter used for controlling emissions from gasoline engines, this removed smoke particulates, cutting them by about 30%.
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 reduced particulate emissions (presumably also increading fuel economy). Individual plungers for each injector were operated by a camshaft through roller followers (both cam and followers were 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. The location and height of the slot exposed to incoming fuel corresponded to the start and duration of injection. When the engine was shut off, the slot closed completely by an electric solenoid on the outside of the pump.
|1994 Ram engines||5.9 V8||Cummins- Stick||Cummins- Auto|
|Horsepower||230 bhp @ 4000||175 bhp @ 2500||160 bhp @2500|
|Torque||330 lb-ft@ 3200||420 lb-ft@ 1600||400 lb-ft@ 1750|
|Redline||5250 rpm||3000 rpm||3000 rpm|
|Battery (std)||600 (750 opt)||Dual 750||Dual 750|
The fuel pump limit on wide-open throttle idle speed was raised from 2875 to 3000 rpm for improved driveability. This control made the high speed fuel cut-off more gradual as well. Dodge claimed the new pump was also more reliable.
A high-pressure piston-type lift pump had greater flow to help cool the high pressure pump. It supplied fuel to the high pressure pump at 211 bs/in2 to assure that the high speed pump was always full. An external priming plunger was included to aid in restarting after running out of fuel.
An improved fuel filter (between the lift pump and high-pressure pump) and larger water separator accommodated the higher fuel flow rate; a new 100-micron strainer between the gas tank and fuel lift pump removed particules, as well. This included a thermostat-controlled fuel heater to prevent 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.
Thanks to the engineering approach to particulate control, the Cummins turbo-diesel retained its eminence among diesel pickup truck engines in fuel economy. Fuel economy was better than in the 1993 Ram pickup, aided by lockup torque converter (automatic), better aerodynamics, and lower rolling-resistance tires. Transmission torque capacity, though, forced Dodge to cut the Cummins’ power somewhat with the automatic transmission.
Throttle response and low speed torque were improved by adding a waste gate to the turbocharger. Low speed torque and throttle response were improved through use of a smaller turbine wheel and nozzle which reached peak boost quickly and at lower engine speed. The waste gate opened at high engine speed to prevent excessive turbine speed which would have been detrimental to turbocharger durability. The waste gate was actuated by intake manifold pressure working against a spring-loaded diaphragm. High altitude performance was unaffected by the waste gate.
To add power, the compressor had MWE (Map Width Enhancement), which recirculated a small amount of compressed 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.
Larger diameter, straighter intake ducting from the turbocharger to the charge air cooler and the charge air cooler to the intake manifold reduced air flow restriction for greater power. The intake manifold elbow was cast aluminum and the ducts were rolled aluminized steel.
A larger charge air cooler (sometimes referred to, somewhat incorrectly, as 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 that further enhanced these capabilities. A revised electronic control schedule shut off heat when vehicle speed exceeded 10 mph.
A 1994 revised combustion chamber "bowl" in the piston crown worked with the injection pump to lower engine-out emissions. The piston ring land above the top ring was narrowed to reduce hydrocarbon emissions. A new combination of ring materials and construction reduced oil consumption. The need to add oil between changes became unlikely.
A larger diameter crankshaft vibration damper was used on engines with manual transmission to compensate for the increased torsional vibration caused by raising the power output.
More rapid engine warm-up and improved cab heater performance resulted from separating the thermostat and "jiggle pin" functions. The new thermostat was sealed at low temperature. A separate jiggle pin unit was threaded into the cylinder head. The jiggle pin, which 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, is more effective than the previous unit in the thermostat.
A longer transmission adapter allowed for addition of a torque converter clutch to the automatic transmission.
The air cleaner was mounted on the right fender side shield and connected to the turbocharger inlet through a hose. To determine when the air filter element should be replaced, the air cleaner included an air flow restriction gauge called the Filter Minder™. The Filter Minder showed when the filter element should be replaced and when it shouldn't. Diesel engines are unthrottled and therefore consume much more air per mile than gasoline engines. This generally means that the air cleaner on a diesel engine will start to restrict engine performance and/ or reduce fuel economy at shorter mileage intervals than on a gasoline engine, but the mileage when deterioration begins varies widely with operating conditions. Furthermore, filter elements which appear dirty, but are not plugged, protect the engine better than new ones by filtering out ultra-fine dust particles.
The Filter Minder determines flow restriction of the air filter by measuring air pressure drop on the "clean" side of the filter. It consists of a diaphragm and calibrated spring inside a sealed, clear plastic cylinder that is plumbed to the air cleaner housing. A disc attached to the diaphragm moved along a graduated air pressure scale on the side of the housing. A drop in air pressure, due to filter restriction, moved the diaphragm and the disc showed the size of the drop. A check valve held the diaphragm and disc at the highest restriction that the filter had experienced. The owner could periodically monitor the level of restriction as it increased throughout the life of the filter. When the ring reached a red zone on the scale, the filter needed to be changed. At that level of restriction, performance started to deteriorate. After the filter element was replaced, pressing a button on the top of the housing resets 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. The engine still had 12 valves with mechanical high-pressure direct fuel injection and conventional, flat hydraulic “mushroom style” tappets.
In 1997, the throttle control system was refined and hydraulic power brake booster was added.
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 (both used high pressure direct injection). 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 not only increased airflow, but allowed for 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 provided more precise, instantaneous control and greater response over the entire power range (up to 3200 rpm).
Additional upgrades include an overhead valve rocker system designed for a minimum of 150,000 miles without adjustment, a redesigned piston for increased power and fuel 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 (it stopped production in December 1999), and a 235-horsepower version that was paired with either the NV4500 five speed or NV5600 six-speed manual.
For the 2001 model year, the 24-valve high-output Cummins turbo diesel were introduced, a 235 hp version and a high output 245 hp version; production started about January 2000. The main difference between the 215 hp and the 235 hp engines was 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. The crankshaft position sensor was removed; the tone wheel on the crankshaft was moved to the camshaft gear on the front of the cam, and the camshaft position sensor was also now used for the engine speed input for timing. The 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, although it was still designated as VP44. The fuel-injection pump gave higher pressure and revised fuel injectors gave higher fuel flow. The turbocharger on the high output model was the old one; the standard output engines used a new turbo with fewer parts.
The engine data plate, on the left side of the gear housing, lists the horsepower, serial number (stamped on the right side of the block above the oil cooler cavity), and other information. (Buyers can find the engine information on the truck VIN; the eighth position is the engine, with the 215 and 235 hp versions of the standard engine coded as 6, and the 245 horsepower version coded as 7.)
2002: new 5.9 liter diesel block and injection
In model-year 2002 (calendar year 2001), a new 5.9-liter High Output Cummins Turbo Diesel was brought out, the most powerful turbo diesel engine in the heavy-duty market (at the time) with 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. This version had a new block and high-pressure, common rail fuel-injection; the average major overhaul interval was 350,000 miles. An inline six, the new 5.9-liter Cummins had 25% fewer parts than typical V-8 diesels; 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 new high-pressure common rail fuel injection systems for the 2003 Dodge Ram Heavy Duty used pilot injection - the injection of a small amount of fuel to start combustion - before the main, power-producing fuel charge is injected, to smooth combustion pressure in the cylinder, cutting noise and providing gas-engine-like cold starting (verified as far down as –40° Farenheit).
A gear-driven fuel pump was electronically controlled and provided pressures up to 23,200 psi (1600 Bar); it was less dependent on engine speed than traditional systems for cleaner combustion and higher low-speed torque with better vehicle response.
For model year 2003 (introduced in 2002), the High Pressure Common Rail version was brought out, rated at 300 hp in the high-output/manual transmission model.
Starting in 2004, a new straight-six common-rail turbo diesel became available in both 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, with a longer certified engine life than Chevrolet or Ford diesels, with an average major overhaul interval of 350,000 miles and 30-40 percent fewer parts than typical V8 diesels.
The high-output Cummins 610 Turbo Diesel used a revised piston combustion bowl and a high-flow, electronically controlled waste-gated turbocharger matched boost pressure with engine needs to reduce emissions and eliminating the need for exhaust gas recirculation, avoiding the need for over 50 components. More to the point for most owners, the 610 had 610 lb.-ft. (827 N•m) of torque starting at 1,600 rpm.
The Cummins turbodiesel durability was due in part to gallery cooled, high-strength aluminum pistons; gallery cooled, high-strength aluminum pistons, high-strength Inconel® exhaust valves and 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. As with the 2002 engine, it had high-pressure, common rail injection.
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
In January 2007, Dodge announced that it would be selling 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 new 50-state-clean diesel included the Bluetec 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 combines with a uniquely designed piston combustion bowl and a high-flow, electronically-controlled Variable Geometry Turbocharger (VGT™), matching boost pressure with the engine’s performance needs to reduce emissions and improve drivability. Within the exhaust system, a self-cleaning DPF and an oxidation catalyst reduces particulate matter by a factor of 10. The emissions system is designed for a government-certified 120,000 miles. A new closed crankcase ventilation system eliminates crankcase fumes and oil carry-over. The Cummins turbodiesel has life-to-major overhaul intervals of 350,000 miles, providing (in 2009) more than a 100,000-mile advantage over the competition. Nearly 40% of the new engine’s parts are carryover, with modifications geared to surpass emissions standards and increase horsepower and torque, while maintaining the durability associated with Dodge and Cummins.
One engineer described Bluetec: “BlueTec is an addon after-treatment system with certain internal engine parameter changes applicable to any 4 stroke diesel. The technology was originally developed by KonTec of Germany. DCX bought them up and [Mercedes] now takes credit for it.” The Cummins diesel used in heavy duty Dodge pickups and in Dodge chassis cab trucks did not use urea or any other diesel emissions fluid in 2010, and the pickup diesels were given an exemption through 2013 (the chassis cabs require 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. This provides high visibility of the sophisticated emissions systems on the Ram, giving dealers a more effective tool for explaining the diesel price increase.”
The new high-pressure common rail fuel injection system used pilot injection—pre-squirting a small amount of fuel to start combustion before the main fuel charge is injected to smooth out combustion pressure, cut noise, and provide near-instant cold starts. 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.
Starting in 2007, a single 6.7 liter Cummins diesel was available, producing 350 hp.
As of 2009, the 6.7 liter Cummins diesel used in Dodge pickups with standard exhaust brake capability had 350 hp and 650 lb-ft of torque with best-in-class low-end torque; it had a 5/100 limited engine warranty and was the cleanest engine in the Heavy Duty segment. A six-speed automatic with two overdrive gears had better launches and gas mileage, and let drivers manually choose gears. Remote start became available. Payload was up to 5,130 lb, with 16,850 lb of towing capacity. For more details, including market share and such, see our Dodge Ram 2500/3500 and Dodge Ram 3500 Chassis Cab pages.
The 6.7 continues to use solid tappets (non-roller) to this day, with an adjustment interval of 150,000 miles.
2011 and beyond
As of December 2010, the Cummins straight-six diesel was still planned for future Rams and was scheduled to be coupled to the eight-speed automatic in 2013-14.
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.
Cummins also makes a V8 diesel, which is the most likely one to be adopted by Dodge. It should get around 18 mpg city, 23 mpg highway in the Ram 1500, producing over 250 horsepower and around 440 lb-ft of torque rpm. This is a very different engine from the B-series straight six, redlining at over 5,000 rpm, operating as quietly as a gasoline engine; it is reportedly being made for use by the military, and should appear around 2013-2014.
The fate of the 4.2 liter Cummins V6 (190 hp, over 400 lb-ft) in Dodge trucks is unknown. Fiat makes diesels in this range, but Cummins has definite drawing power.
Cummins makes Tier 4 engines in four and six cylinder versions ranging from 75 to 751 horsepower. The 75-173 horsepower range four and six cylinder QSB engines use existing 3.3, 4.5, and 6.7 liter platforms with a fully integrated air intake to exhaust after-treatment system, with cooled EGR and compact catalyst, along with a direct flow air filtration system, variable flow turbo, and efficient coalescing filter in the PCV system.
Urea / DEF and the Cummins engines, post-2010
“JeepMover” wrote in May 2011: “The Cummins has no urea until 2013. Reason? We built up credits by meeting 2010 emissions, in 2007. ... Did you know that to change the glow plugs and do other repairs on the diesel Fords, the entire cab has to be lifted off?” That said, the move to using urea in 2013 resulted in a (roughly) 5% increase in gas mileage, according to Cummins.
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! (On the systems I'm familiar with, the NOx sensor downstream of the SCR catalyst is part of this check.)
SCR should increase cooling capacity by reducing the need for EGR, and the engine can be retuned for less PM creation and decrease the need for DPF regenerations. Theoretically the fuel economy should improve too.
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!