Rivet Counter N Scale EMD SD70IAC, Norfolk Southern/America250/Freedom (Eagle) #250

When it comes to building locomotives, drastic changes to a locomotive design typically occur only out of necessity. General Motors’ Electro-Motive Division (EMD) began building the SD70M/SD70MAC family of locomotives during the early 1990s, and these locomotives were powered by EMD’s latest 16-cylinder prime mover, the 710G3C.

In 1997, the federal Environmental Protection Agency’s emission standards for diesel locomotives were released, resulting in necessary changes by specific times to meet the looming Tier-level criteria set by EMD.

The first Tier level for new locomotives to meet, beginning in 2001, was the Tier 1 standard for new locomotives off their respective assembly lines. EMD managed to meet this criterion by simply changing the cooling systems on the SD70M/SD70MAC line of locomotives. These changes included modifying the carbody to have flared radiator sections harkening back to the SD45 days.

Tier 1 was a moderately easy hurdle for EMD and the SD70 family. Tier 2, however, would take some work. One option that EMD had for Tier 2 requirements was to dust off the plans for the four-stroke 265H prime mover from the, ultimately, failed SD90MAC and continue its development. The other option was to create an all-new platform based on the current SD70M and 710G3C prime mover.

In the spring of 2003, 4 SD70ACe demonstrators rolled out of EMD’s London, Ontario plant, debuting the new model of the SD70 family. Externally, the locomotive was reminiscent of the SD90MAC-H Phase II locomotive. The squared-off cab, the angular engine hood profile, the large flared radiator, and tapered dynamic brake section at the rear give these locomotives their one-of-a-kind appearance.

The prime mover for the SD70ACe locomotive was still the venerable 16-cylinder 710G3C 2-stroke engine, which had been further successfully modified to meet Tier 2 compliance standards and thus dubbed the 710G3C-T2. This version of the prime mover was rated for 4,300 horsepower.

The prime mover would go on to be further modified to meet Tier 3 compliance in the early 2010s, which would also see a bump in horsepower to 4,500.

Beneath the locomotive, the SD70ACe rides on EMD’s radial HTCR-4 truck or non-radial HTSC-2 truck, which both can contain either 42- or 43-inch wheels depending upon customer specifications. Mounted between the trucks is the locomotive's 4,900-gal fuel tank.

In 2004, CSX’s 20 pre-production units, numbered 4831 - 4850, were built to help EMD flush out assembly challenges and for further testing and demonstration purposes on various railroads. With no limitations for service type, CSX pushed the units into all areas of the railroad while on home rails, and other roads did the same, such as Montana Rail Link.

To further add to the catalog, in the fall of 2004, EMD released 3 SD70M-2 locomotives which would become the replacement for the SD70M model. Externally identical to the SD70ACe, the SD70M-2 is the DC-powered sibling of the AC-powered SD70ACe. Not to be confused with the “Dash 2” electronics implemented in the diesel locomotives' Second Generation, in the instance of the SD70, the “-2” simply stands for Tier 2 compliance. Much in the same way, the “e” in SD70ACe stands for enhanced.

Interestingly enough, GM74 was initially released with SD70DCe on its builder's plate before quickly being changed to SD70M-2.

With official orders beginning to be placed in 2005, the SD70ACe and SD70M-2 locomotives cemented EMD’s updates and improvements to the ever-popular SD70M and SD70MAC as the next generation of EMD power. Being a top-selling locomotive through 2014, and a bit beyond due to various railroads' use of Tier 4 credits, more than 2,700 examples of the locomotives have been built for the US, Canada, Mexico, and Australia. And gaining a second lease on life, some units have even reached the age of being rebuilt to continue plying the rails.