08/04/2026
Before the Go-Devil, the engine that would power the Jeep couldn't run for more than 22 hours at 3,400 RPM without failing. It made 48 HP from 134 cubic inches and had the durability of a lawn ornament. In 1938, Willys-Overland hired Delmar "Barney" Roos as vice-president of engineering. Roos was born in the Bronx, held dual degrees in mechanical and electrical engineering from Cornell, and had worked at Pierce-Arrow, Studebaker, and Rootes in England. Willys gave him a dying four-cylinder that dated back to the 1926 Whippet and told him to make it survive. Roos redesigned the bearings. Added a pressurized oil delivery system. Installed aluminum pistons. Counterbalanced the crankshaft. Replaced the 57-pound flywheel with a 31-pound unit. Redesigned the valve springs. The reborn engine ran for 100 hours at 4,400 RPM on the dynamometer and produced over 60 HP. Same 134 cubic inches. Same bore and stroke. An engine that had been obsolete became an engine that could go to war.
The Go-Devil L-134 displaced 134.2 cubic inches (2,199 cc) from a 3.125-inch bore and a 4.375-inch stroke. Extremely undersquare: the pistons traveled nearly an inch and a half farther than the bore was wide, which produced enormous low-RPM torque relative to the displacement. 60 HP at 4,000 RPM and 105 lb-ft at 2,000 RPM. Compression: 6.48:1, low enough to run on whatever fuel was available in a combat zone, including captured enemy gasoline and aviation fuel mixed with whatever was on hand. L-head flathead valvetrain: valves beside the cylinders, operated directly by the camshaft through short lifters. No pushrods. No rocker arms. Nothing to adjust. Nothing to break above the block. Three main bearings supporting the crankshaft. A single-barrel Carter downdraft carburetor. The entire engine weighed 365 pounds bare. A soldier with a wrench, a screwdriver, and a basic understanding of how a four-stroke engine works could maintain it in the field. That was the point.
In 1940, the U.S. Army solicited bids for a light reconnaissance vehicle. American Bantam submitted the first prototype, but the company was too small to manufacture at scale. Willys-Overland submitted the Willys Quad, powered by the Go-Devil. Ford submitted the Ford Pygmy. All three were tested. The Army chose the Willys design primarily because of the engine: the Go-Devil produced more power per pound than either competitor's powerplant. Willys won the contract. When production was consolidated in 1942, Ford manufactured exact copies of the Go-Devil engine (designated GPW) alongside Willys' MB production. Between 1941 and 1945, more than 647,000 Jeeps were built: over 359,000 Willys MBs and over 277,000 Ford GPWs. Every one of them was powered by a Go-Devil L-134. The engine crossed North Africa, Italy, France, Germany, and the Pacific. It ran in mud, sand, snow, jungle heat, and Arctic cold. It pulled artillery. It carried wounded. It towed trailers. It powered generators. It did everything the Army asked, running on bad fuel in impossible conditions, maintained by 19-year-old kids who had been mechanics for six months.
