Weighing in at more than 400,000 pounds and with a length in excess of 80 feet and massive 4,300 horsepower tractive effort, the SD90/43MAC is one of the heaviest, longest, and most powerful single diesel locomotives in the world. To date, there have been three production “versions” of the SD90MAC. The SD90/43MAC was originally designed with a 6,000hp engine in mind, but was fitted with a smaller and more reliable 4,300hp engine that ended up being kept that way by most railroads, even though the option to upgrade to the higher horsepower engine was offered at a later date.