Editor’s note: The 1980s was a transition period for engine technology in America. The iconic carburetor gave way to fuel injection. Cubic inches were out, and liter designations marked a new era for engines — one when power and fuel economy were no longer mutually exclusive. This modern engine age has featured some of the best innovation, technology, and performance yet.
#10 – Jeep 4.0L Straight-Six
You’ll be hard pressed to find a more passionate tribe of engine loyalists than those who worship at the automotive alter of the beloved 4.0L I6 (often referred to as a straight-six).
This little engine that could is best known for reliably powering a variety of Jeep utility vehicles from 1986 through its phase out in 2006. But the famed inline-six lived an entire life before Chrysler stamped its name on it. The modern straight-six engine was born in 1964 after American Motors Co. built it to power a variety of AMC passenger cars and Jeep vehicles, as well as a number of International Harvester light-duty trucks (International Harvester bought the engines from AMC for Scouts, Travelalls, and other pickups.)
The “modern” 4.0L was introduced in 1986 for the 1987 model year and has been “bulletproof.” It’s widely recognized as one of the best engines ever built, often performing dutifully for upward of 300,000 miles. The 4.0L I6 kicks out 190 horsepower from a 242 cubic-inch cast-iron block and cylinder head, hydraulic lifters (with non-adjustable rockers), and seven main bearings.
In 1991 and beyond Jeep applications, the engine was fuel injected which, according to Jeep Tech, helped it perform “much better in off-camber, bouncy, and steep situations. It also calibrates better for changes in altitude. Fuel economy is also improved.”
- Bore x Stroke – 3.88” x 3.41”
- Displacement – 242 (4.0L)
- Compression Ratio – 8.8:1
- Torque – 220 ft.-lbs. at 4,000 rpm
If you own a 4.0L, there are plenty aftermarket parts to keep it running as strong — or stronger — than ever. According to Summit Racing, here are some of the more popular items for the engine: