Of the three prototype jeep designs of 1940, the Willys-Overland fielded the most powerful engine, but that advantage was largely negated by it being in heaviest vehicle. Being well over the Army’s weight limit nearly cost Willys the opportunity to bid, and only political intervention kept them in the game. Predictably, the Army’s unrealistic weight limits moved upward, and by the time Willys’ July 1941 low bid was accepted for the first contract, the standardized design weighed as much as the original Willys prototype. Thusly, the Willys 134ci Go-Devil four-cylinder engine became the heart of the jeep and part of the legend. Had Ford or Bantam won the bid, it’s very likely their final designs would also have had a bigger engine by necessity.
Willys’ part in the story might have been different had it not been for Delmar G. “Barney” Roos. Willys-Overland hired Roos as chief engineer in 1938, and Roos had an enviable resume. His automotive career began in 1912 working for Locomobile (then Timken Axle), Pierce Arrow, Marmon, Studebaker, and Rootes in England. He was noted as a great “engine man” and had created several notable designs. Short fused and impatient, he was a tough guy to work around, but Roos was an undeniable mover, shaker, and hard driver.
Job one for Roos was to redo the anemic Willys four and do it on a budget. The Willys four had appeared in the 1926 Whippet, which was the company’s first economy car, albeit an upscale one. It displaced 134.2 ci, just like the later Go-Devil, but only made 30 hp. By the late ‘30s, the Willys four was making 48 hp with a few upgrades, but it had become notoriously unreliable and was well under the market’s power curve.
Roos’ reliability benchmark was 100 hours at full power. One of his first tasks was to strap the 48hp engine to a dyno. It lasted 22 hours at 3,400 rpm—’nuff said. Roos and his staff set to modernizing the engine, incorporating insert bearings, a fully counterbalanced crankshaft, aluminum pistons, a fully pressurized lubrication system, and a revised valvetrain. In just a few months, the new engine was ready for the dyno. It exceeded 100 hours at over 60 hp at a whopping 4,400 rpm. Success! The new engine was dubbed Go-Devil and first appeared in some of the 1939 Willys cars rated at 61 hp at 3600 rpm. In 1940, when the stylish new Willys 440 (4-cylinder, 1940) models appeared, they were all powered by the Go-Devil, as were the ’41 441 and ’42 442.
Later in 1940, Roos spearheaded Willys’ entry into the 1⁄4-ton military game. The Go-Devil was ready for prime-time, but the rest was a clean-sheet workup. One of the crucial parts of the company’s involvement was Roos’ decision to push for the bigger engine despite the weight penalty. A smaller engine was seriously contemplated, but Roos’ choice was vindicated later when the standardized jeep had gained the weight needed to be the durable machine the Army wanted.
The Go-Devil lived a long life. It lived in Willys cars prior to WWII, was mounted in military jeeps from ’41 to ‘52, used in civilian 4x4 Jeeps from ’45 to ‘54 and in the DJ 4x2 Jeeps through ’64. The Jeep station wagons and trucks used them until mid-’50s, and they were also used as commercial, marine and stationary (generator) engines.
The Go-Devil was not used in the short-lived post-war Willys Aero cars but was used in the Kaiser Henry-J from ’51 to ‘55 and its Sears clone, the Allstate. These engines featured a 7:1 compression ratio, uprated intake system and were rated for 68 hp and 109 lb-ft of torque—the highest stock ratings the Go-Devil achieved. The Go-Devil was in U.S. production at least into 1965 and was built under license in France, Japan and Argentina. The mid–’50s-and-up F-head four—also a Roos design—was largely based on the Go-Devil, and it lived on through 1971. That particular engine will be a subject for a future Jeep Encyclopedia.
Specifications: Willys Go-Devil, L134 engine
Production Dates: 1938-1965
Type: Inline four, L-head
Displacement: 134.2 ci
Bore & Stroke: 3.125 by 4.38 in
Gross Power: 60-68 hp @ 4,000 rpm
Net Power: 54 hp @ 3,800 rpm
Torque: 105-109 lb-ft @ 2,000 rpm
Compression Ratio: 6.48:1 (7.0:1 in some applications)
Engine Weight: 365 lbs (bare)