GMC 426 Inline 6: The Forgotten Engine That Powered Super Duty Trucks

Most truck enthusiasts know about GMC's legendary 478 V6, the Twin-Six V12, and the famous Jimmy engines. But almost nobody remembers the GMC 426. Introduced in 1939, the GMC 426 cubic-inch inline-six was built for one purpose: moving enormous loads. It powered GMC's original Super Duty trucks decades before the Super Duty name became associated with Ford, helping haul gravel, construction materials, and industrial cargo across America during a transformative period in the nation's history. In this video, we explore the forgotten story of the GMC 426, the heavy-duty AC770 and AC870 Super Duty trucks it powered, and the engineering philosophy that made this 7.0-liter workhorse so effective. With its massive 5-inch stroke, seven-main-bearing block design, and torque peak arriving at just 1,000 rpm, the 426 wasn't designed for speed—it was designed to work. We'll also look at GMC's Group 3 engine family, including the 361, 451, and later 477, and examine how these engines helped shape America's highways, construction projects, and industrial expansion throughout the 1940s and 1950s.. Subscribe for more forgotten engines, rare truck history, industrial machinery, and automotive stories that deserve to be remembered. #gmc #truckhistory #inline6 #vintagetrucks #superduty #classictrucks #automotivehistory #heavydutytrucks