Over 50 years ago, while the general public’s attention was riveted on the space race, agriculture was fixated on a horsepower marathon.Farmers, hungry for larger tractors, not only demanded bigger engines but also yearned for related technological advances in transmissions and hydraulics as well as creature comforts such as quieter air-conditioned cabs.Anticipating this need for stout power plants, International Harvester had invested heavily in new engine design coming out of its Melrose Park development center.True to form, the company’s highly talented engineers didn’t fail in that task; they turned out completely new six-cylinder diesel platforms comprising what would become a line of famous engines — the models D-360 (naturally aspirated), D-414 (naturally aspirated and turbocharged), and D-436 (turbocharged).All told, this effort accounted for a $25 million investment in design as well as tooling and manufacturing.The engines were rugged to a fault, employing seven main bearings. Among the many advances incorporated into their design were jet-cooled pistons, advanced fuel-injection pumps, torsional vibration dampers, and plateau-honed centrifugal cast-iron wet-type sleeves.These features and manufacturing techniques, along with engineering devoted tocreating rugged engines, established these diesels as standards in the industry.Thus was created the legendary “bullet-proof ”IH diesels so considered because of their outstanding durability. Still today, reconditioned D-436 engines, for example, are highly sought after, bringing $5,000 or more.Big engines, new transmissionsPutting all the power generated by these new diesels to work challenged IHC engineers even further. Noted for developing and then launching in 1969 the first successful hydrostatic transmissions for tractors (dubbed the Hydrostatic Drive) an elite team of designers set to work upgrading the company’s slide-gear units.In their place was created a four-speed synchromesh transmission that featured shift-on-the-go capability under load. International Harvester’s famous torque amplifier was offered as optional equipment with the new synchromesh transmissions.Topping off power transfer advances was a new modular final drive with the planetary final drive and axle carriers housed in one unit that bolted to the sides of the differential housing main rear frame. This approach provided an especially rugged final drive structure that was also easier to service.