Cummins has a history of producing strong, long-lasting diesel engines, including some of the most popular ones for on-highway applications. Two of their engines in particular, the N14 and the ISX, continue to remain popular diesel choices.

So what make the two different from each other? Why did Cummins make the switch from the N14 to the ISX applications? In this article, we dive into the history and the differences between the engines.



Prior to the release of the N14, the NTC was the workhorse of the Cummins line. For a while, it was really one of the best over-the-road engine applications. It had two versions: a small cam with a diameter of under 2 inches, and a larger cam to help support the increasing injector pressures.

They also began putting electronics in the engine, resulting in two different NTC applications with electronic systems—the PT Pacer, which had a cruise control system, and the Pace unit, which included a cruise control system with a PTO setting (this means you could select the engine RPM and it would sustain it no matter the load, up to a certain point).

Cummins eventually got their electronics and parts people together in the same room with the goal of creating a 1,000,000 mile engine. The N14 was the result. It has the same cubic displacement as the NTC, but included more electronics, like the injectors.

After a while, though, the EPA began to release new emissions restrictions and standards that the N14 couldn’t meet. Cummins needed to move to an Integrated Management System, which was full electronics. This became the base for the ISX, which would replace the N14 as the Cummins workhorse.


In order to meet these increasing restrictions, they really needed to increase pressure to better atomize fuel, which would then result in better emissions. So they worked to improve the electronic fuel controls that would appear in the ISX, allowing the engine to meet the EPA guidelines.

A few years later, though, the EPA came out with even stricter emissions guidelines, and in order for the ISX to continue to meet standards, Cummins really had to control fuel injection, making it more precise. This led to the production of the common rail injectors.

The ECM controls the timing of these injectors, leading to more precision, and the rail keeps the pressure constant. This increases efficiency and kept the ISX in line with EPA regulations.

Despite this development, though, the exhaust was still “dirty” and produced a fair amount of soot. They then came out with after treatment (DPF), which acted like a sponge that collects soot. If it cracked, it was easy to tell, as black would begin to leak out.

In 2013, in order to clean exhaust even further, though, diesel exhaust fluid (DEF) was developed. After the exhaust goes through the DPF, the DEF molecularizes it, cleaning it even further. The DPF would heat the catalytic converter. The chemically produced heat of up to 1,200 degrees would burn the carbon to reduce the volume of soot. This helped result in clean stacks—if there’s black soot on your stacks, your system is broken.



While the N14 does include some electronic components, the ISX has more. It’s name is even based on this (IS stands for Interact System). This move toward more electronic controls is what allowed the ISX to continue to meet the EPA regulations


The two engines are physically different in size. Two versions of the ISX were involved in the phase out of the N14 and the M11 (the little brother of the N14, which was likewise unable to meet emissions standards), the ISX12 and the ISX15.


Because of the shift to electronic controls, the N14 has more valve train components than the ISX. To learn more about valve train components, read our blog post on the topic. This reduction in the amount of components likewise reduced a lot of possible wear. The ISX is more of a direct injection type of device than the N14.

Despite their shared history in the Cummins lineup, the N14 and ISX are very different engines. Both have their pros and cons, though, leading to operators having strong feelings about one or the other.