AMC Straight-4 engine

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

Development
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 engine
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.

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

Applications


This engine was used in the following vehicles:
 * 1984–1986 Jeep CJ-7
 * 1983.5–1984 AMC Eagle
 * 1984–2000 Jeep Cherokee (XJ)
 * 1986–1992 Jeep Comanche (MJ)
 * 1987–2002 Jeep Wrangler (YJ/TJ)
 * 1988–1989 Eagle Premier
 * 1996–2002 Dodge Dakota