3rd Generation Cummins 5.9L and 6.7L Specs

I love Dodge. I’ve had a good relationship with those guys - Robby Gordon 

Just like Robby Gordon, Cummins has an incredible, mutually beneficial, and rewarding relationship with Dodge. Together they changed the face of the truck manufacturing business forever, and while their association with Dodge put Cummins on the worldwide motor map, Cummins saved Dodge trucks from oblivion. 

It’s a story for the diesel ages that has weathered all sorts of adversity, including RAM’s separation from their parent company, that still endures to this day. And it all began with the introduction of the first generation five-point nine liter Cummins motor and its placement in the engine bay of a Dodge RAM.

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But by the time the third generation Cummins began to emerge in two thousand and three and went on to power RAM trucks for another six years until two thousand and nine, the first generation motors and the trucks that they pulled down the road were, in automotive terms at least, and as desirable as they still are, ancient truck history.

When they made their debut, the third generation Cummins motors, which still used the same twenty-four valve five-point nine liter power plants developed for the previous generation were bolstered by new technology and innovation that included the introduction of a common rail fuel injection system, that thanks to Dodge’s new body configuration, which included the first of the RAM’s Mega Cabs, are still incredibly sought after vehicles by the RAM and diesel faithful.  

The Third Generation Cummins 5.9L

When Cummins rolled out their third generation five-point liter motor, they’d ironed out all the kinks that the previous incarnations had, and by electing to remain with the twenty-four valve set-up that was introduced during the latter half to the second generation motors life, they had a stable platform to work with.

Their endless desire to innovate and improve on the previous generation saw the third incarnation of Cummin’s motor take a massive leap forward and increased the power that the second iteration had produced by a staggering sixty horsepower and more than fifty foot-pounds of torque.

The motors were, thanks to Cummins’s attention to detail, not only more powerful than previous years top of the line High Output models but were also much quieter and thanks to them running far more cleanly, much kinder to the environment. 

Adopting Common Rail Technology

Whole common rail fuel injection systems weren’t considered cutting edge technology by the automotive industry in two thousand and three, it was the first year that Cummins had opted to, and began to use the system in one of their motors.

Electronically controlled, common rail was designed to increase fuel efficiency as it distributes fuel much more evenly throughout the injectors. Working in conjunction with an electronic fuel lifter and CP3 injection pump, its new common rail injection system allowed Cummins’ motor to do the sort of things that its engineers had always known it could, and it once again transformed the way that the truck that it powered was seen by both it’s already established and devoted fanbase and the average joe looking for a more credible vehicle.  

The main advantage of common rail though, at least as far as Cummins was concerned, was that it helped them to delay the introduction of an exhaust gas recirculation system for an additional forty-eight months, which gave them a chance to further perfect it before introducing it to their motor.  

The Third Generation Fuel Injection System

The introduction of high-pressure common rail, also meant that Cummins had to strip back and redesign the rest of their fuel injection system, which led to the introduction of the previously mentioned CP3 pump and new ECM (engine control module) controlled injectors, which while not being as durable as the mechanically operated system that they replaced, were more efficient.

As they worked to perfect their motor, Cummins also reduced the number of nozzles that the injectors in their motors used from eight in two thousand and three to five in two thousand and four, to ensure that the system always operated at peak economy regardless of how hard it was being pushed.

Turbocharging The Third Generation 5.9L Cummins

Since they’d introduced a turbocharger to their motor, Cummins had stuck with a name that they trusted, Holset and they didn’t see the need to change the brand of turbochargers that they used when they introduced their third-generation motor.

Starting in two thousand and three, the five-point nine was fitted with a HE341CW turbocharger which used a mechanically controlled internal wastegate, that served to divert excess waste gas from the turbine, which meant that it was able to spin up more easily and do exactly what it was supposed to without being damaged by an unregulated flow of gas from the motor. 

However, halfway through two thousand and four, Cummins elected to swap the mechanically controlled Holset turbocharger for an electronically uprated version (the HE351CW), which due to the way it was controlled, improved both the efficiency of the motor and the power that it made. 

The Third Generation 5.9L - Power, Torque And Towing

Due to Cummins’s habit of constantly redesigning their motor, the performance figures of the RAM range that it powered vary from year to year and according to the transmission that it was coupled to. Between two thousand and three and two thousand and four, the motor was making three hundred and five horsepower and producing five hundred and fifty foot-pounds of torque. 

But by the end of its life as the RAM power plant of choice, thanks to Cummins changing the injection system and the turbocharger that the five-point nine used, it was making three hundred and twenty five horsepower and producing six hundred and ten foot pounds of torque.

The motor modifications resulted in a massive differential in the weight that the motor was capable of towing, and depending on the model (either a 2500 or a 3500), the transmission (automatic or manual) and body style of the truck, between two thousand and three, and the final year of the five point nine’s production life in two thousand and seven,  the motor was capable of towing anywhere between twelve thousand five hundred pounds and fifteen thousand pounds. 

All Change - The Introduction of the 6.7L

In two thousand and seven, everything changed. The regulations governing diesel emissions were becoming increasingly stringent and to ensure that RAM trucks could compete on an equal playing field, and better, their rivals, and stay one step ahead of the EPA (Environmental Protection Agency) and CARB (California Air Resources Board), Cummins went all way back to the drawing board and completely redesigned their motor.

To keep pace with the increasingly hard emissions regulations, Cummins made sure that all of their new motors were fitted with an EGR (exhaust gas recirculation) system and a DPR (diesel particulate filter).  

And both have been mainstays of the Cummins motor ever since. While they were initially susceptible to blockages, which could lead to a reduction in the motor’s performance, over time the development of both has meant that these problems remain firmly in the past. 

The Third Generation Cummins 6.7L - Bigger Is Better

While it didn’t make an appearance until the end of the third generation motor’s lifespan, the six point seven was, and is the motor size of choice that Cummins would continue to, and still continues to, use to power RAM trucks.

Because they were increasing the size of the motors bore and its stroke, Cummins had to completely redesign the block. As the cylinder pressures were, and are higher in the six-point seven than they were in the five-point nine, Cumins opted to use Siamese cylinder bores in the engine block. 

Even though the engine block is considerably different, due to the higher pressure of the cylinders, it’s also far more prone to head gasket failure than the previous five-point nine-liter version of the model was.

That said, regular maintenance and changing the gaskets at one hundred thousand mile intervals can and does, prevent head gasket failure from ever being an issue that any RAM owner should ever have to worry about. 

Turbocharging the 6.7L Third Generation Cummins

Because of the need to bring the motor in line with the tough emission regulations, Cummins was finally forced to follow in Ford and GM’s footsteps and began to use a variable geometry turbocharger, and so began using the Holset HE351VE.

While they had been reluctant to adopt a VGT (variable geometry turbocharger) up until this point, even Cummins had to not so reluctantly admit that it increased the power that the motor made, reduced the emissions that it produced, and improved the driveability of the trucks that it was fitted in.

The biggest advantage of VGT was that it introduced turbo braking to the RAM range, which greatly reduced the trucks stopping distance and can, and in some cases does, extend the life of a truck’s brakes if they’re used to frequently tow a lot of weight. 

One thing that a lot of drivers discovered about trucks using VGT was that, in order to blow clear the blockages that the turbo can be plagued by, trucks that it’s fitted to need to be driven as aggressively as possible, as often as possible.  Which was one of the many reasons why the motor has found favor with and is beloved by, the diesel community. 

Changing The Fuel Injection System. Again.

Increasing the size of the motor meant that Cummins had to, once again, redesign the fuel injection system that it used. 

While they elected to keep the high-pressure common rail system and CP3 electronic fuel pump that the previous five-point nine had used, they had to increase the size of the whole system by just over fifty percent to cope with the increased power of the motor. 

Again, it was a case of Cummins following the age of the mantra of “the more things change, the more they stay the same”  in order to deliver the power and efficiency that RAM demanded from their trucks. 

Emissions Control - Stepping In Line And Saving The Planet

The main reason for Cummins’s redesign was, as has already been mentioned, the need to ensure that RAM’s motors would, and did fall in line with the tougher emissions controls that both the EPA and CARB had set.

To do this Cummins fitted the six point seven with an EGR (exhaust gas recirculation) system which forces the waste gas that the motor produces back into the turbo and the motor and helps to reduce emissions and improve the power that the motor makes. 

The other component that helps to reduce the emissions that the motor produces is the DPF (diesel particulate filter) which captures the solid carbon (often seen as black smoke that flows out of the tailpipe) that the motor makes and burns it.

Even though they’re incredibly efficient and help to save the future, DPF’s are frowned on by certain quarters of the diesel community as they completely eliminate the production of black smoke. Nevertheless, that didn’t stop the third generation Cummins motor from earning its place in the diesel hall of fame. 

The Third Generation 6.7L Cummins - Power, Torque and Towing 

Like the five-point nine-liter that preceded it, the horsepower that the third generation six point seven was capable of making largely depended on the transmission and body style that it was coupled with and fitted into. In two thousand and seven, the first year that it appeared, the six-point seven fitted with both an automatic and manual transmission produced three hundred and twenty horsepower and made six hundred and ten foot pounds of.

But by two thousand and nine, the last year that the third generation motor was fitted into RAM trucks, the manual transmission version of the motor produced three hundred and twenty horsepower and six hundred and twenty foot pounds of torque, while the motor that was coupled with an automatic transmission made a staggering three hundred and fifty horsepower and produced six hundred and fifty foot pounds of torque.

The huge variation in the amount of torque that the motor produced according to the transmission that it was coupled with and the body style of the truck that it was fitted into, meant that the weight that the six point seven could effectively tow was also subject to a massive discrepancy.

The 2500 Quad Cab fitted an automatic transmission that debuted in two thousand and seven could pull thirteen thousand pounds, while the 3500 SRW version of the Quad Cab that appeared in two thousand and nine could easily tow seventeen thousand pounds,