Cummins B Series: In-Depth Review and Analysis

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The Cummins diesel engines have helped to build the American landscape for over 40 years, but what makes them so popular among classic truck lovers?

The Cummins B Series is a family of diesel engines produced for nearly four decades since 1984. Known for their placement in Dodge/RAM trucks, they can also be found in service and school buses. Cummins B-Series engines have been offered in inline-four and inline-six-cylinder configurations.

When Dodge added the Cummins turbo diesel in 1989, the announcement could not have arrived at a better time for the Ram pickup line. For years, sales of Dodge trucks had lagged behind competitors significantly as consumers embraced the newly redesigned GM and Ford pickups. (Ford had introduced its eighth generation F-Series with a 6.9L diesel engine in 1987, moving to the 7.3L IDI diesel engine in 1988. Chevy offered their 6.2L diesel engine, also naturally aspirated with indirect injection). Knowing that it could not continue to operate without a competing diesel engine, Dodge looked for a way to separate itself from the pickup owners who depended on their trucks daily. Cummins provided just the boost Dodge needed as sales improved dramatically. The new 5.9L direct-injected turbodiesel V6 revolutionized the pickup truck landscape, helped save the day for Dodge RAM, and began a legacy for over forty years. Let’s look closer at the Cummins B-Series engines and why they are such a sturdy workhorse on the American landscape.

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Overview Of The Cummins B Series Engine

While the Cummins diesel might have begun in the mid-eighties as an agricultural motor for use in Case tractors and harvesters, it wasn’t long before Dodge tapped the company to fashion a diesel motor for their light/medium-duty pickup trucks. Cummins had experience producing diesel engines for almost seventy years (founded in 1919). Still, their success had been largely on the commercial side rather than the personal truck market. The project was a tremendous undertaking for both Dodge and Cummins and represented a unique opportunity for both companies to promote the power of diesel and sell more trucks.

Over the years, the six-cylinder B-Series diesel appeared in three primary versions, and at over 1100 lbs, it was a hefty motor that looked more like a tractor motor than a truck engine. The Cummins featured a cast iron block, iron cylinder heads, and a strong steel forged crank with seven main bearings. The engines had gear-driven cams, direct injection (rather than glow plugs), and early Cummins engines had a Bosch-style injection pump. A Holset turbocharger provided the primary power boost, enabling the six-cylinder to produce as much power and low-end torque as many V8s.

5.9L Cummins “12-Valve”

The 5.9L Cummins “12 Valve” was the first diesel engine used in a Dodge RAM truck. The 6BT engine was produced from 1989 - ‘98 and offered as an engine option for the RAM 250. The 1991 sales brochure claimed the new engine offered “exceptional fuel efficiency, quick acceleration, excellent towing capacity, and strong high-altitude performance.” Dodge sweetened the pot for potential buyers by providing a seven-year/100,000-mile warranty on the new engine.

The engine produced 160 hp and 400 lb-ft of torque with a compression ratio of 17.5:1, which gave the Dodge truck incredibly low torque for towing. Dodge found that installing the Holset turbocharger could boost the six-cylinder’s power levels to match other V8s, but where the diesel scored points was in the fuel mileage it provided. Owners got the torque and load capacities of V8s but saved money in fuel, which made many truck owners take a hard look at the Dodge. Combined with the idea that diesel engines lasted much longer than their gas-powered cousins, it made them attractive alternatives for some owners).

Early Cummins engines are popular among classic truck owners even though many components might seem archaic compared to today's more sophisticated engines. Owners can generate real power boosts with relatively easy upgrades like turbos, larger injectors, or better fuel pumps.

The Specs Of 5.9 Cummins “12 Valve”

The following list of specifications is for the 5.9L Cummins engine.

Engine Item Engine Specification
Production 1989 - ‘98
Horsepower 160 - 230 hp
Torque 400 - 440 lb-ft
Aspiration Turbo-charged
Camshaft drive Gear driven
Cooling System Capacity 6 gallons
Compression Ratio 17.5:1
Injection Direct injection w/ mechanical Bosch Injection pump
Bore 4.02 inches (102 mm)
Stroke 4.72 inches (120 mm)
Block Material Cast iron
Head Material Cast Iron

5.9 ISB Cummins “24 Valve”

The Cummins engine was updated for a new generation in 1998, primarily because Dodge was under the gun to meet new emissions standards. The engine carried the same displacement, bore, and stroke as its predecessor but was expanded into a 24-valve engine (four valves per cylinder). The ISB (Interact System B) was an electronically controlled engine with a sophisticated ECU and electronic Bosche fuel injection system replacing the mechanical version Cummins had built on the turbodiesel they had been using. The addition of the electronic management system meant that the fuel economy could be monitored more closely, providing better power while still bumping up fuel savings.

The initial ISB Desiels could produce adequate horsepower at 215 - 235 hp, depending on whether the truck had an automatic or manual transmission. Dodge continued to tweak the motor, and in 2001, Dodge offered both a standard and high-output version. The standard 5.9L ISB produced 235 hp, while a manual transmission offered the more potent 245 hp and 505 lb-ft of torque. The higher output ISB had more robust components, with a higher compression of 17.3:1.

In 2003, Dodge converted to a Bosch high-pressure common rail fuel injection system, which provided a power boost. The engine was known as the 5.9 ISB CR and produced 305 hp and 555 lb-ft of torque. When MotorTrend awarded the Heavy-Duty RAM pickup with its 2003 Truck of the Year award, customers began to flock toward the brand. (Ford switched the 7.3L to the horrible 6.0L in a rush to compete with Dodge’s potent diesel). In 2004, Dodge upgraded the ISB again with the Cummins 600, which produced 325 hp and 600 lb-ft of torque.

The Specs of the 5.9 ISB Cummins Engine

The following list of specifications is for the 5.9L ISB Cummins engine.

Engine Item Engine Specification
Production 1998.5 - 2007
Horsepower 215 hp - 355 hp
Torque 420 - 600 lb-ft
Aspiration Turbo-charged
Camshaft drive Gear driven
Cooling System Capacity 6 gallons
Compression Ratio 17.2:1 - 17.3:1
Injection Electronic Direct injection w/ high-pressure electronic Bosch Fuel pump
Bore 4.02 inches (102 mm)
Stroke 4.72 inches (120 mm)
Block Material Cast iron
Head Material Cast Iron

6.7L ISB Cummins Engine

In mid-year 2007, Dodge introduced the 6.7L ISB Cummins engine, which is the latest version. The engine has been used in Dodge 2500/3500 pickups. It differs from the earlier ISB engine because it has a larger bore and stroke (4.18 X 4.88) and produces around 350 hp and 650 lb-ft of torque. (The engine was updated in 2020 to produce 400 hp and 1000 lb-ft of torque). With the 6.7L Cummins, the Variable Geometry Turbocharger (VGT) helped boost power output numbers to greater levels.

The Specs Of The 6.7 ISB Engine

Engine Item Engine Specification
Production 2007.5 - present
Horsepower 350 hp - 400 hp
Torque 650 - 1000 lb-ft
Aspiration Variable Geometry Turbocharged
Camshaft drive Gear driven
Cooling System Capacity 6 gallons
Compression Ratio 19.0:1 - standard
16.2:1 - High Output
Bore 4.22 inches (107 mm)
Stroke 4.88 inches (124 mm)
Block Material Cast iron
Head Material Cast Iron (Sensor Hole Style)

What Were Some Of The Issues With Cummins B Series Engines?

The Cummins B series engine has undoubtedly helped make Dodge/RAM trucks the powerful workhorses that most of us know them to be. And as great as these engines have been (and are), there are some issues that classic truck owners should be aware of.

Killer Dowel Pin

Early 5.9L Cummins turbodiesels have a pin pressed into the engine block above the timing cover. The pin is notorious for falling into the timing gear and seriously messing up the engine. The dowel pin has a purpose (to adequately align the timing gear housing to the engine). Fixes are available, and companies like XDP make a bolt-on kit preventing this. If you plan to use an older 5.9L or 5.9L ISB in your project, you want to ensure the fix has been done.

Defect In “53” Block

The 1999 - 2000 5.9L ISB Cummins suffer from an occasional casting defect that leads to a loss of engine integrity. (Look for the number “53” imprinted into the side of the block). Additionally, the exhaust valves on the 24-valve Cummins have been known to crack in higher mileage situations.