Usually, when we talk of automotive legends, we talk about legendary cars of the past. Cars that set the template for an entire segment or redefined performance and design. Sometimes, some of the most legendary cars are loved for their engines, and nothing else. But once in a while, manufacturers produce an engine so great that its identity is no longer tied to a single car. Think the Porsche Flat-six, Chevy Small Block V8, or the Honda B-Series.
In the world of pickup trucks and diesel engines, that rare legend is the Cummins 5.9-liter or the 6BT. Originally designed for industrial and commercial use, this turbo-diesel engine was built to be a reliable workhorse. But soon enough, it changed the game for pickup trucks, earning a cult following along the way for its simplicity, durability, and performance. Even today, it’s still revered by truck owners and diesel enthusiasts as the ultimate diesel engine. This is the story of how the Cummins 5.9-liter became the most respected diesel engine in truck history.
The Cummins 5.9-Liter Turbo Diesel Was A Game Changer For RAM
Back in 1984, Cummins debuted the 5.9-liter turbocharged inline-six diesel engine, purely for commercial use. In 1989, the engine, dubbed B-Series, found its way into Dodge RAM pickup trucks, revolutionizing the segment and creating one of the most legendary automotive partnerships. Since then, the Cummins 5.9-liter has become one of the most loved powerplants ever produced, both for those using their trucks for work and pickup enthusiasts.
The Cummins 5.9-liter engine featured a beefy cast-iron block with forged crank with seven mains, a gear-driven cam drive, and a 12-valve cast-iron head. Such an architecture meant the 5.9-liter was designed to withstand years of commercial abuse without breaking a sweat or seal. Unlike Ford and General Motors’ V8 powerplants, this inline-six engine was the only one to use direct fuel injection, courtesy of Bosch. Add to that its Holset H1C turbocharger, and the 5.9-liter became a powerful and fuel-efficient powerplant, ideal for pickup truck applications.
With its segment-leading performance, fuel efficiency, and absolutely bulletproof reliability, the 5.9-liter engine revolutionized the pickup truck segment. It even helped Dodge RAM boost its sales numbers, attracting new owners who moved from gas-powered models to Cummins-powered engines. While the 5.9-liter may no longer be on sale today, it’s a benchmark when it comes to truck performance and durability. And even today, enthusiasts are willing to pick one up for the love of it, despite having more powerful options in the market.
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So Reliable, There’s A Million-Mile Club For Eligible Owners
Enthusiasts care about performance, families about practicality, but commercial truck owners have to worry about durability. That’s what made the Cummins 5.9-liter so special during its multi-decade run, with plenty of examples of even older Cummins still running strong with nothing but basic maintenance. These engines were built to take a beating and still keep running, and with proper maintenance, they can even outlast the surrounding truck!
Unlike other so-called “reliable” vehicles, where reaching a million miles is a one-off achievement, the Cummins 5.9-liter does it often enough to have a dedicated club. Yes, Cummins has a Million-Mile Club, and it’s not as exclusive as you’d think. Perhaps the most notable member of the club is Howard Clayton, who drove his 2000 Dodge RAM 3500 to an impressive 2.6 million miles! One of the more recent entrants to the club is Harry and Shirley Albach, who drove their 2001 Dodge RAM 3500 to 1,020,000 miles.
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Segment-Leading Performance With Insane Tuning Potential
Apart from its durability, the Cummins 5.9-liter-powered RAM pickup trucks have become popular for their performance, too. Left alone, this engine produced plenty of power, and in its first iteration, it delivered class-leading 160 horsepower and 400 pound-feet of torque. With many updates along the way, the Cummins 5.9-liter eventually belted out 325 horsepower and 610 pound-feet of torque in its last iteration before discontinuation. And it balanced this performance with fuel economy, something that was uncommon during the time of gas-guzzling pickups.
The Cummins diesel was powerful enough, but today, enthusiasts have found that it can be pushed to extreme performance limits, too. With enough modifications, this workhorse diesel engine can turn into a powerful engine that can be used for off-road, on-road, and race applications. For example, a simple remap, a bigger turbo, and higher-flow injectors can unlock up to 600 horsepower and 1,000 pound-feet of torque from a Common Rail ISB example. Many tuners have even unlocked up to 1,500 horsepower and 2,000 pound-feet with more comprehensive tuning!
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Evolution Of The Cummins 5.9-Liter Inline-Six Engine
The history of the Cummins 5.9-liter diesel engine is fascinating, too. Back in the day, Cummins engines were all the rage in agriculture, long before they made their debut in pickup trucks. In 1984, Cummins debuted the 5.9-liter 6BT engine, which was designed for industrial and agricultural applications. But thanks to its performance and fuel economy, it attracted the eyes of non-farmers and workers alike. So, by 1989, Chrysler had begun plonking this workhorse engine in Dodge RAM light-duty pickup trucks.
Cummins 5.9-Liter 12-Valve (6BT) Changed The Game
With the new 5.9-liter 12-valve engine, Dodge RAM sales went through the roof. This engine was paired with a five-speed manual or a heavy-duty A727 three-speed automatic, and unlike other diesels of the time, the 5.9-liter featured direct injection and a turbocharger. As a result, it produced 160 horsepower and 400 pound-feet of torque, while offering bulletproof reliability and excellent fuel economy. This combination is what made it such a popular engine during its time.
|
Years |
Horsepower |
Torque |
Displacement |
|---|---|---|---|
|
1989 – 1998 |
160 – 215 HP |
400 – 440 LB-FT |
5.9 liters |
Second-Generation 5.9-Liter Followed In 1994
In 1994, Cummins introduced the next generation of the 5.9-liter engine, which carried over the same displacement, engine block, connecting rods, and head. However, it brought a new Bosch P1700 inline injection pump, improving fuel delivery and performance. The new Cummins 5.9-Liter produced 175 horsepower and an impressive 420 pound-feet of torque. To no one’s surprise, truck owners loved this newly modified engine, too; so much so that many truck owners even installed the second-gen 5.9-liter in their older trucks.
Third-Gen Came In 1998 With VP44
Four years later, Cummins yet again updated the 5.9-liter engine, now called ISB5.9, with 24 valves, i.e., four valves per cylinder, and electronic engine management. These changes improved airflow, combustion efficiency, and power output, boosting the power to 235 horsepower and 460 pound-feet of torque. Another update to the engine was the VP44 injection pump, which offered even better fuel control than before.
|
Years |
Horsepower |
Torque |
Displacement |
|---|---|---|---|
|
1998 – 2007 |
215 – 325 HP |
420 – 610 LB-FT |
5.9 liters |
Fourth-Gen Soon Followed With Common Rail Injection
The next big update came in the early 21st century, in 2003, when Cummins introduced a common rail fuel injection system to the legendary 5.9-liter engine. This injection system allowed for more precise fueling, which produced a smoother engine character while improving fuel economy and reducing emissions. It also boosted the output to 325 horsepower and 610 pound-feet of torque, making it the most powerful engine in its class at the time. The performance boost made it an even better workhorse engine and forced other manufacturers to take notice, too.
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Legacy And The Present-Day Cummins 6.7-Liter Diesel
The 5.9-liter diesel engine was discontinued in 2007. Cummins wanted to deliver more power and meet stricter emissions norms, so the 5.9-liter was no longer a feasible platform for it. So, it made way for the 6.7-liter Turbo Diesel for pickup trucks. The new, bigger diesel engine had 13 percent more displacement and plenty of new tech, which helped it beat the 5.9-liter in terms of power output. In 2013, Cummins introduced a number of performance updates, including the Selective Catalyst Reduction (SCR), which delivered 10 percent better fuel economy and more peak torque while doubling the engine’s oil change intervals.
The 6.7-liter Turbo Diesel still retains the familiar cast iron block and cylinder heads of the 5.9-liter engine, but comes with advanced fuel and air delivery and a healthy dose of performance boost. It now produces up to 420 horsepower and 1,075 pound-feet of torque, with the latter being delivered as low as 1,700 RPM. Cummins also says the current turbo diesel powerplant is quieter and more powerful than ever. And like its predecessor, the 6.7-liter still promises to be the go-to workhorse that can last for a million miles, tow an airplane, and beat sports cars in a drag race (with the right mods, of course).
Still, enthusiasts today would pick the older Cummins 5.9-liter B-Series turbo diesel engine. This is the powerplant that blazed the way for the likes of the 6.7-liter and other modern truck engines. It raised the bar of performance for 3/4 and one-ton pickup trucks and commercial chassis cab applications. And there are plenty of examples where it has outlived the trucks it came on. That’s the reason why the original Cummins diesel remains so highly sought-after today by both diesel enthusiasts and RAM fans. It may have come as part of mediocre trucks, but the 5.9-liter was anything but that.
Source: Dodge, Cummins, Bring a Trailer