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The Best Jeep Engines And Weirdest Factory Motors Ever Produced

Did Your Favorite Jeep Engine Make The Cut?

Jeep engines powered the Gladiator

Jeep engines have been powering off-road dreams for more than 60 years. Who hasn’t thought about crashing through the underbrush and throwing mud in a Jeep? Many Jeep engines have come and gone over the years; some good, others trash. Today, we want to take a look at the history of Jeep and several of the best engine units that the company has ever produced or worked with.

History of the Jeep

As with many innovations, Jeeps came into existence because of a war. The United States War Department knew by the late 1930s that it may eventually become embroiled in a war in Europe. Knowing that made the Army feel an urgent need for an updated fleet of light battlefield vehicles. To that end, the War Department developed a set of specs and submitted them to 135 U.S. automotive manufacturers on July 11, 1940. Manufacturers were given 11 days to submit bids, 49 days to build their first prototype, and 75 days to have 70 test vehicles built. On top of such a short turnaround, the specs were pretty daunting. They included: 4WD, seating for at least three, a wheelbase of 75 inches (later upped to 80 inches), have a fold-down windshield, a payload capacity of 660 lbs, the engine had to be capable 85 lb-ft of torque, and the vehicle had to have a dry weight of less than 1,300 lbs. The Army found that the weight limit was unattainable, so raised it to 2,160 lbs.

Only three manufacturers were able to develop a bid for the vehicle in time for the deadline. American Bantam Car Company and Willys-Overland Motors made the 11 day deadline for bids. Ford Motor Company was allowed to submit late, rounding out the threesome. American Bantam won the bid because it was able to commit to building a prototype within 49 days, but could not build Jeeps on the scale the Army needed. That opened the door for Willys and Ford to be allowed to submit their prototypes late. After much testing and having bought 1,500 copies from each manufacturer, the Army awarded the end contract to Willys-Overland, mainly because of its strong engine. Basically, the entire history of the Jeep was determined by how strong the first Jeep engines were. That brings us to the first entry on our list of the best Jeep engines, the L134 Go Devil.

Willys L134

The first Willys Jeeps (the MB) were not available to the public. However, by 1945 Willys was able to switch production from military applications to civilian vehicles again. The first civilian model was the Civilian Jeep (CJ). Semantics being semantics, the first units made available to the general public were the CJ-2A. It was powered by the L134 Go Devil engine.

The Go Devil had a displacement just over 134 cu in and had an L-head (valves parallel to cylinders) design – hence the L134 designation. The version in the CJ-2A had a bore of 3.125 inches (79.4 mm) and a stroke of 4.375 inches (111.1 mm). Willys used an undersquare engine so that peak torque would be available at lower rpm. By today’s standards, output was low at 60 hp and 105 lb-ft of torque, but that was pretty impressive in 1945. The best feature of the CJ-2A was its durability. If the Army could torture it on the battlefield, imagine how tough this engine was.

327 Vigilante

In 1965, Kaiser Jeep, the successor of Willys-Overland, sourced a 327 V8 from American Motors Corporation. To be clear, AMC built this 327 five years before Chevrolet built its more famous 327. Nicknamed the ”Vigilante” by Kaiser-Jeep, this engine was essentially a bored out version of the 287 engine that had been powering the AMC Rambler since 1961. The bore was increased to 4.0 inches (102 mm) and the engine was equipped with hydraulic valve lifters. These Jeep engines were used in the Jeep Wagoneer and Gladiator pick-up truck between 1965 and 1967.

Dauntless 350

The Dauntless 350 was built by Buick and was used in the Jeep Gladiator and Jeep Wagoneer from 1968 through 1971. Buick 350’s were built differently than other GM 350’s of the era. Buick versions used a deep-skirt cast iron block, an external oil pump, a forward-mounted distributor, and were undersquare. The oil pump mechanisms of these Jeep engines were housed in an integrated aluminum timing cover, so the oil filter was exposed for added cooling. These engines were highly prized for their durability and power and were often modified for hotrods of the era.

AMC 401

We are still stuck in the 70’s with this next engine. The AMC 401 is probably one of the better-known Jeep engines and can still be found conquering many roads and mud trails today. The AMC 401 can be found in some 1971-1979 Jeep Wagoneers, Cherokees, J-10’s, and J-20’s. It has a displacement of 401.11 cu in and in 1971, a stock engine was capable of 330 hp. That number, however, was dialed back to meet emissions and fuel efficiency regulations from 1972 on. The AMC 401 uses a forged steel crankshaft and connecting rods for added durability. These engines are fairly rare because emission controls, insurance rates, and high gasoline prices at the time caused AMC to limit the models that were equipped with the 401. The rarity of the engine combined with its toughness and excellent power output means that these Jeep engines are highly sought after.

AMC 4.0L

Fast forward to the 1987 model year and we come to the inline 6 cylinder AMC 4.0L. These Jeep engines can be found in late model YJ’s and TJ Wranglers, Comanches, Cherokees, and early Grand Cherokees. The first AMC 4.0L has a bore of 3.875 in (98.4 mm) and a stroke of 3.414 in (86.7 mm), so it has a displacement of 241.6 cu in. It has an output of 190 hp and 220 lb-ft of torque. The torque is available at lower rpms, making this a great engine for off-road antics. The AMC 4.0L was held over after Chrysler bought the Jeep line from AMC.

The 4.0L engine is likely the best known of all the Jeep engines ever produced. By the time it was discontinued in 2006 more than 7 million units had been sold worldwide and many owners have reported driving more than 300,000 miles without having to rebuild their 4.0L Jeep engines.

2.5L I4

In the late 80s and through the 90s, Jeep went through a phase where the company wanted to attract more daily drivers to the Wrangler line. The automaker attempted to do this by adding fuel efficiency and comfort. Fuel efficiency was tackled by offering a 2.5L inline four-cylinder engine in the YJ and early base TJ Wranglers. This engine can also be found in some Cherokees and Comanches as well. At the end of production, this engine was capable of 130 hp and 150 lb-ft of torque. Like many Jeep engines, the 2.5L surprised people with its long-term durability and low-end power. There are a few people who have trashed it because it is a four-cylinder engine, but it seems they have forgotten that the first Jeeps were all powered by four-cylinder engines.

3.8L V6

For the 2007 through 2011 model years, the Jeep JK Wrangler was powered by the 3.8L EGH V6. These Jeep engines are a bored out version of the 3.3L V6. The bore is 3.78 inches (96 mm) and stroke is 3.43 inches (87 mm), creating a 3,778 cc (231 cu in) powerplant. Output varied over the production life of the engine, but the last engines built were capable of 215 hp and 245 lb-ft of torque. This engine is tougher than buyers expected when it was first introduced. Its great torque curve makes it perfect for off-roading. The only reason that Jeep went away from this engine was to meet government regulations for efficiency. The 3.6L V6 that replaced it just isn’t as good, though.

Well, there you have it, our list of the best Jeep engines ever produced. But what about the weirdest? The above engines are fantastic beasts, but fairly vanilla when compared to these unusual weirdos below.

6 Weird & Unusual OEM Jeep Engines

Over the years Jeeps have been powered by a variety of engines, some of which were pretty unusual. Here’s a look at 6 of the oddest Jeep motors.

The Jeep brand has had high times and low times, largely depending upon what other company owned them at the time. Thankfully each of its owners saw the value in the Jeep brand and keep the wheels rolling, even if it meant borrowing an engine or two from another company.

1979 Jeep DJ5G

Believe it or not there was a Jeep that shared an engine with a Porsche. The 2.0 L overhead camshaft four-cylinder engine was purchased  from Audi/Volkswagen from 1977 through 1979. It was the same basic engine as used in the Porsche 924 and 924 Turbo. However, the engines sent to America were built to AMC specs, which are different from Audi/VW/Porsche specifications. AMC used a carburetor and standard points ignition and were built to  wider internal tolerances. The result was that the AMC version produced up to 30 hp less than the VW-Audi-Porsche version of the engine. While  installed extensively in the AMC Gremlin, AMC Spirit, and AMC Concord, the only Jeep in which this engine was installed was the 1979 Jeep DJ (Dispatcher or Postal Delivery). In the DJ5G, it was mated to a 3-speed A904 automatic transmission with a VW/Audi pattern bellhousing.

M422 Mighty Mite

If you think that AMC didn’t start building Jeeps until its purchased Kaiser, you’d be wrong. American Motors won the contract in 1960 to build a compact, lightweight (1700 lbs) M422 “Mighty Mite” vehicle for the Marine Corps. It was powered by a 1.8 L AMC designed aluminum air-cooled V4 engine that produced 55 hp.The Mighty Mite was commissioned by the Marines as their helicopters were not capable of lifting full-sized Jeeps. However, advances came quickly and soon the Marines had heavy-lift capabilities (bye, bye Mighty Mite).  The Mighty Mite was in production for just 36 months and only 3922 were built.

Renault J8S Turbo Diesel

So we’ve seen a German-made engine in a Jeep, how about  a French-made diesel? The Renault  2.1 L four-cylinder turbodiesel (not a pure diesel design but adapted from a gas engine) was optional in Jeep Cherokee and Comanche  between 1984 and 1986. Even now you can find folks who love the engine (particularly the high mileage it delivered) to those who didn’t (issues with easily overheating the all-aluminum diesel engine). It was fairly sophisticated for its time and that may have been the reasons for some its issues. Plus problems pretty much across the board with the French-made Peugeot transmissions didn’t make many friends and the whole fiasco probably set back the adoption of small diesels in SUVs in the US for several years.

Kaiser Dauntless V6

Here’s an engine that powered an IndyCar to a 232 mph qualifying speed for the Indianapolis 500 some years ago. In 1966, Kaiser introduced the “Dauntless” 3.7 L V6 engine for the CJ and as an option in the C101 Jeepster Commando. But it hadn’t started out as a Kaiser engine. The company had purchased the rights and tooling  to build the 3.7 L engine from Buick, as GM no longer felt there was a market for V6-powered cars. It remained in the Jeep line until 1971,  not long after AMC acquired Kaiser in 1970. Then in 1974, realizing the need for a mid-sized motor, GM purchased all the mothballed tooling back from AMC and had the line running within four months. GM kept that version of the engine in production until 1987, building a special version to comply with the Indianapolis 500 stock block rules, and with additional modification taking its life as a production car motor out to 2008.

Willys L134 (Go Devil)

The Willys engine that powered nearly every Jeep used in WWII, regardless of which company manufactured the vehicle, had both humble and unlikely roots. Before the war, Willy’s four cylinder engine powered the Model 77, a very inexpensive, but high mileage car (sort of the Chevrolet Spark of its day). The engine was an under performer, producing only 48 hp from 145 CID. The company wanted the government contract so in a relatively short time redesigned the engine to produce 60 hp from just 134 CID and nicknamed it the “Go Devil”. Despite the fact Willy’s entry was overweight, the Army was so impressed by their entry’s performance, they were awarded the contract.

Jeep Tornado

The Jeep Tornado was the first U.S.-designed  overhead cam (OHC) automobile engine that was mass-produced after WWII. The 3.78 L inline-six was introduced in mid-year 1962. The Tornado replaced the flathead 6-226 Willys Super Hurricane that had been in service since 1954. However, its life in the US was brief, being dropped from the line after 1965. The engine was too sophisticated to maintain for mechanics accustomed to working on flatheads. The engine did continue in production in South America. When Ford acquired Willys-Overland do Brasil, they made design changes on the engine, so what had started as a Kaiser-Jeep engine was for a few years a Ford engine.


About Chris Riley

I have been wrecking cars for as long as I've been driving them, but I keep coming back for more. Two wheels or four, I'm all in. I founded GearHeads.org and then built and ran AutoWise.com until selling it to Lola Digital Media in 2020. I look forward to watching AutoWise grow as part of the AllGear group.