MTH ELECTRIC TRAINS

In the horsepower race of the 1990s - which turned out to be a passing fad - the Holy Grail became a 6000 hp diesel. But neither EMD nor GE had a prime mover capable of being upgraded to that size. As a stopgap measure, EMD added four cylinders to its proven model 710 engine to create the 5000 hp, 20 cylinder, 80 foot long SD80MAC in 1995. Conrail was the only taker, rostering all 30 units produced and later passing them on to successor CSX.

Other railroads waited for EMD to deliver its all-new power plant, the 6000 hp "H" engine, EMD's first four-stoke diesel. When the H engine was delayed, EMD offered what was intended to be a temporary solution: its new SD90MAC locomotive, designed for the H engine but temporarily powered with a 4300 hp, 16-cylinder model 710 engine. The hybrid "SD9043MAC" was externally the same as the SD80MAC and sold rather well - much better than the 6000 hp version when it finally arrived. As it turned out, American railroads decided a 4300-4400 hp diesel was a more versatile building block for multiple-unit consists, and the craze for 6000 hp engines faded. The SD9043MACs were never upgraded to the H engine. Today most 6000 hp SD90MACs are gradually being withdrawn from service while the "temporary" 710-powered SD9043s soldier on. And while the H engine was not a great success in the United States, it has gained a foothold in China and other overseas markets.