AMC Straight-4 engine

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


 * For an outline of all engines used by AMC see

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 6-cylinder and the new engine, the 4-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."

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 inches (99 mm) and de-stroked to 3.188 inches (81 mm). The block is basically the same as the legacy 258-cubic inch 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 Jeep. It was produced through 2002 for the Jeep, 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 (89 kW) at 5400 rpm and 145 ft·lbf (197 N·m) of torque at 3250 rpm using sequential multiple-port Fuel injection (MPFI). For comparison, the 258 I6 provided 112 hp (83.5 kW) at RPM and 210 ft·lbf (285 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 to 1995, it produced 130 hp (97 kW) horsepower and 149 ft·lbf (202 N·m) of torque with 9.2:1 compression in the Cherokee and Comanche. Allpar

Applications
This engine was used in the following vehicles:
 * 1984-1986 Jeep
 * 1983.5-1984 Eagle
 * 1984-2000 Jeep
 * 1986-1992 Jeep
 * 1987-2002 Jeep (YJ/TJ)
 * 1988-1989 Eagle Premier
 * 1996-2001 Dodge Dakota