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The American Motors Corporation straight-4 engine was used by a number of AMC, Jeep, and Dodge vehicles from 1984-2002.

DevelopmentEdit

American Motors devoted three years to the development of a new four-cylinder engine. According to Jeep's chief engineer, Roy Lunn, "unlike most engines available today [it] was not designed for passenger cars and then adapted for trucks. We specifically developed it with our Jeep vehicles and Eagle in mind. That's the reason that performance and durability were of such prime consideration from the very beginning." Although some of components were interchangeable between the AMC 258 cubic inch six-cylinder and the new engine, the four-cylinder was not a cut down version of the big six. Noted Roy Lunn, "There is some common competency, but the 4-cylinder includes many unique items such as its own electronics systems. It also has a shorter stroke and larger bore. The valves are larger and the pistons are new." Roy Lunn recalled: "We wanted as much displacement - for power and torque - as possible within the confines of bore centers of the tooling. The only parameter we could influence substantially was stroke. So we picked the largest bore and stroke in order to get 2.5 Liters."[1]

The AMC 150/2.5 L engineEdit

The 2.5 L inline-4 was a shortened version of the 258 6-cylinder engine bored to 3.875 in (98.4 mm) and de-stroked to 3.1875 in (80.96 mm). The block is basically the same as the legacy 258 cu in (4.2 L) engine with a larger bore and the two center cylinders removed. The head featured a new combustion chamber and port design that was later used on the 4.0 L — the 2.5 L I-4 head was stretched by two cylinders in the center.

Instead of the standard AMC bell housing bolt pattern, AMC/Jeep engineers adopted the General Motors small V6 and four-cylinder bolt pattern (commonly used with GM's transverse-mounted powerplants) for their new engine, because the new AMC 2.5 replaced the four-cylinder engines that had been purchased from GM; and because AMC continued to buy the 2.8 L V6 from GM until the 4.0 L I6 was introduced in 1987. The four-cylinder and V6 shared the same drivetrain components, whereas stronger transmissions were needed for the new 4.0 L.

The AMC I4 first appeared in 1984 with the new XJ Cherokee. It was produced through 2002 for the Jeep Wrangler, as well as for the Dodge Dakota pickup that also used the AMC/Jeep designed four since 1996.

AMC 150/2.5 Specifications
Bore x Stroke 3.875 in x 3.875 in
Displacement 150.4 CID (2,464 cc)
Valvetrain eight valves (overhead)
Main bearings five
Compression ratio 9.1:1 to 9.2:1 depending on year

Output the final year was 121 hp (90 kW) at 5400 rpm and 145 lb·ft (197 N·m) of torque at 3250 rpm using sequential multiple-port fuel injection (MPFI). For comparison, the 258 I6 provided 112 hp (84 kW) at 3200 RPM and 210 lb·ft (280 N·m) of torque at 2000 rpm in its final year with the computer-controlled carburetor.

For several years, the engine was detuned for the Wrangler; from at least 1992-1995, it produced 130 hp (97 kW) and 149 lb·ft (202 N·m) of torque with 9.2:1 compression in the Cherokee and Comanche.[2]

AMC 150/2.5 Compression Horsepower Torque
One-barrel carburetor 9.2:1 105 hp at 5,000 132 lb-ft at 2,800
Throttle body injection (TBI) 9.2:1 117 hp at 5,000 135 lb-ft at 3,500
Multi-point fuel injection (MPFI) 9.1:1 120 hp at 5,250 139 lb-ft at 3,250

Note that the TBI system was made by Renix and used from mid-1986-August 1990.

ApplicationsEdit

1992 Jeep YJ AMC I4 engine

2.5 L AMC Straight-4 in a 1992 Jeep YJ

This engine was used in the following vehicles:

See AlsoEdit

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