Class I railroads currently employ both the 16-cylinder 7FDL and 12-cylinder GEVO-12 prime movers in their GE locomotives.Д®MD locomotives on Class I railroads employ four different engine designs, the 567, 645, 710, and 1010J prime movers. Wabtec has used the four-cycle 7FDL design since the mid-1950s, then switching to the GEVO prime mover domestically in the mid-2000s. On Class I railroads, rosters are predominantly a two-builder affair, with Wabtec (formerly General Electric) and EMD locomotives dominating the Class I rosters. From the cooling system to the traction motors underneath, everything is balanced to work well with a specific horsepower output. Since the same prime mover can produce different power amounts, a locomotive design is tailored to support a prime mover producing a particular horsepower output. Some can be built with different features to increase horsepower, such as a turbocharger. Chris Guss photographД®ach prime mover can be rated at different levels of horsepower or built with a different number of cylinders. A rebuilt EMD 16-cylinder 645 prime mover is installed on a Norfolk Southern SD40-2 in Altoona, Pennsylvania. Prime movers provide enough power to pull both the locomotive, any freight cars attached to it, while also producing enough extra output to support the power needs of the various systems on the locomotive such as headlights, computer systems, and cooling fans. Locomotive prime movers are the engines inside all diesel-electric locomotives and are the heart of the entire locomotive.