After turning the diesel world on its head with their first-generation five-point liter motor, when it was time to find a new power plant for the next series of pickup trucks that Dodge introduced in nineteen ninety-four, they decided to follow the old adage about not needing to fix something if it wasn’t broken and stuck with Cummins and their five-point nine-liter workhorse.
But Cummins being Cummins worked their mechanical magic and between nineteen ninety-four and two thousand and two, the diesel motor that sat under the hoods of most of Dodge’s trucks was the upgraded second-generation five-point nine-liter version of the original motor.
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During its eight-year history with Dodge, the second generation motor underwent a significant overhaul, and in nineteen ninety-eight, Cummins changed their motor from a twelve-valve unit to a twenty-four valve model.
While the second-generation motor that Dodge used in their trucks between ninety-four and ninety-eight wasn’t entirely dissimilar to the previous motor, the twenty-four valve version that came into service during the last four years of its life, followed in the footsteps of the first generation motor and roared straight into the diesel hall of fame.
2nd Generation Cummins 5.9L - The Twelve Valve Version
The main issues that Dodge wanted Cummins to address head-on with the second generation motor were emissions and power.
Dodge wanted to reduce the former and increase the latter, and so Cummins went to work.
They designed a new fuel injection system that used a p-pump injection system (which became known as the “little engine within an engine”), a brand new turbocharger, and a much bigger intercooler which significantly reduced the emissions that the motor produced and substantially enhanced the power that it made.
5.9L Twelve Valve Fuel Injection
Even though the fuel injection system was completely redesigned by Cummins to be more efficient than the previous version, the most important part of the new injection system and the main reason why diesel lovers still talk about it as though it was the second coming (which, technically it was) was the ‘p-pump’ that made it work.
Patented by Bosch, it’s a mechanical pump that significantly increases the amount of fuel that the injector forces into the motor, which improved its performance and increased the power that it made.
Using the upgraded fuel injection system also meant that Cummins had to alter the design of the fuel bowl, which was re-engineered to work in conjunction with the new fuel injection.
One of the major aspects of this system that continues to make it so desirable was, and is, the ease with which the p-pump can be swapped for a new, even more, efficient version, which can, and will, increase the fuel flow rate and increase the power that the motor makes.
The Twelve Valve Air Induction System
In order to improve the performance of their five-point nine-liter motor, Cummins used a larger intercooler and a turbocharger fitted with a wastegate (which regulates the amount of exhaust gas flowing over the turbocharger’s turbine and ensures that it remains within peak operating range and doesn’t produce too much boost which could damage the motor) to maximize the amount of air being forced into the motor and improve the power that it made.
Cummins initially used the same turbocharger that they’d used on their first-generation motor, the Holset H1C, but boosted its performance by adding the aforementioned wastegate.
At the end of the first year of production, nineteen ninety-four, Cummins changed the turbocharger they used on the motor and swapped the older model Holset for a newer model, the HX35.
Updated and upgraded just like the Cummins motor that it was fitted to, the newer turbocharger was more robust and durable than the previous version and could easily cope with pressures of anything up to forty psi (pounds per square inch).
Twelve Valve Power, Performance And Towing
As is often the case, the horsepower, and torque that the initial twelve-valve version of the Cummins produced varied according to the transmission that it was coupled with and the model of truck that it was fitted into.
But, between nineteen ninety-four and nineteen ninety-eight, the second generation motor produced between one hundred and sixty (in the entry-level trucks that used an automatic transmission) and two hundred and fifteen (in the high spec. Manual transmission trucks) horsepower.
Likewise, in the base model automatic trucks the motor generated four hundred foot-pounds of torque while in the higher-end manual trucks it made four hundred and forty foot-pounds of torque.
What was surprising, was the amount of weight that the motor could tow, which was anywhere between thirteen and a half thousand pounds when it was fitted in 2500 models and fourteen and half thousand pounds in the 3500 models that were fitted with a manual transmission.
It never ceases to amaze us how such large differences in towing weight can be attributed to body style and size and mere forty-foot pounds of torque.
Even More Surprising…
That’s right, there’s something even more surprising about the twelve-valve version of the second generation Cummins engine, and that’s how much racers and competitive towing drivers adore it.
Because of its relative simplicity, it’s an incredibly easy motor to tune and with a few simple upgrades, it’s possible to up its horsepower to close to four figures and more than double the amount of torque that it can make.
The engineers at Cummins really know what they’re doing and those sort of numbers always make us wonder what they could do if the big wigs in charge removed their shackles and let them go wild. Now that would be a motor for the ages.
The Twenty Four Valve Changes: 1998 - 2002
Behind the scenes, Cummins was increasingly busy and they had big things in mind for their second-generation motor, all of which arrived in the form of the twenty-four valve version of their power plant which replaced the already much loved twelve-valve version.
Doubling the number of pistons per cylinder (up from two on the twelve-valve to four on the twenty-four valve) meant that Cummins had to make some serious mechanical changes to their motor, which meant altering the fuel injection system and most notably the way the motor was configured.
While the higher number of valves meant that the throttle response improved and coolant flow increased, it also meant that the engine block had to be redesigned, and to accommodate the higher valve count, Cummins made the walls that separated the motor compartments thinner, which in turn made them far more prone to cracking when the motor was pushed to its absolute limits.
The Fuel Injection System
More valves meant more change, and the first thing that Cummins did was to take out the Bosch p-pump system that had worked so well with the twelve-valve version of the motor and replace it with an electronic injection system (known as the VP44) which was supposed to work in close collaboration with the ECM (engine commutated motor) to regulate and precisely control the amount of fuel that was injected into the five-point nine.
And ninety-nine point nine nine nine recurring times out a hundred, it works incredibly well, but the addition of an electric lift pump that was supposed to constantly monitor and adjust the fuel pressure is responsible for the point zero zero zero one times that it does fail and is a noted weakness in an otherwise nearly flawless motor design.
It Isn’t All Bad News - The Air Induction System
This is the one part of the motor that continued to subscribe to Dodge and Cummins’s “if it ain’t broke, don’t fix it” philosophy and they retained the same intercooler and Hoster HX35 turbocharger that the twelve-valve version of the motor used.
One of the most radical changes that occurred during the twenty-four valve version of the second generation five point nine-liter motors service life with Dodge was the addition of a High Output model to the range of pick-ups.
This variation used a brand new six manual transmission to wrangle even more power from the Cummins motor, and while it can’t compete with the jaw-dropping Aisin automatic transmissions that brand new top of the line RAM trucks use, between nineteen ninety-nine and two thousand and two, the High Output six-speed manual transmission managed to squeeze an additional ten horsepower and forty-five foot-pounds of torque out of the second generation motor.
Power, Performance And Towing - The Twenty Four Valve Guide
We know that it seems like we’ve come down a little hard on the twenty-four valve version of the second generation Cummins, but we just wanted to highlight some of the errors and mistakes that we think Cummins made during the switchover, and even though they did get some things wrong, they got much more right.
Those additional twelve valves made a lot of difference in the performance stakes and by the end of two thousand and two, depending on the transmission that the motor was coupled to, the five-point nine liter second-generation motor was producing between two hundred and fifteen and two hundred and forty-five horsepower and generating between four hundred and forty and five hundred and five foot-pounds of torque.
The higher numbers, were, of course, the amount of power that it made when the engine was coupled with the High Output six-speed manual transmission that Dodge and Cummins designed specifically to work with the second generation motor.
It really is incredible what Cummins managed to achieve with the addition of an extra twelve valves. And a brand new fuel injection system.
Twenty Four Valves Of Towing Power
While drag and track racers don’t have the same level of respect for the later period second-generation Cummins five point nine as they do for the motor from the first four years, the twenty-four valve beast has proved itself to the everyday diesel devotee time and time again.
The additional torque that the makes gave it an increased towing capacity, and even the lowliest of quad cab 2500 trucks were, and still are capable of pulling thirteen thousand four hundred pounds of weight behind them.
But the real towing surprise and the twenty-four valve version of the 3500 truck that diesel fanatics all over the country still lust after is the High Output six-speed transmission version, that when coupled with the second generation Cummins five-point nine-liter motor can tow fifteen thousand one hundred pounds of weight behind it without breaking a sweat and while cruising comfortably at fifteen hundred rpm.