AMC straight-4 engine

AMC straight-4 engine
2.5 L AMC straight-4 with MPFI
Overview
Manufacturer	American Motors (1984-September 1987) Chrysler (September 1987-2002)
Also called	PowerTech
Production	1984–2002
Combustion chamber
Configuration	Straight-4
Displacement	150.4 cu in (2,465 cc)
Cylinder bore	3.875 in (98.4 mm)
Piston stroke	3.1875 in (80.96 mm)
Cylinder block alloy	Cast iron
Cylinder head alloy	Cast iron
Valvetrain	OHV
Compression ratio	9.1:1-9.2:1
Combustion
Fuel system	Carburetor Renix Throttle-body fuel injection Mopar Sequential multi-point fuel injection
Fuel type	Gasoline
Oil system	Wet sump
Cooling system	Water-cooled
Output
Power output	105-130 hp (78-97 kW)
Torque output	132-150 ft·lb (179-200 N·m)
Chronology
Predecessor	GM Iron Duke engine Chrysler 2.2 & 2.5 engine
Successor	Chrysler 1.8, 2.0 & 2.4 engine

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

Development

American Motors devoted three years to the development of a new four-cylinder engine.^[1] The brand new engine was designed to use AMC's existing spacing between the cylinder bores so that the tooling remained the same.^[2] The location of other major components, such as the distributor, oil filter, and starter were also kept the same to so as to use the machine tools for the AMC straight-6 engine.^[2]

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 are some common parts, 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]

Design

The AMC 150/2.5 L engine has a bore of 3.875 in (98.4 mm) and a stroke of 3.1875 in (80.96 mm). The head features a combustion chamber and port design that was later used on the 4.0 L — the 2.5 L I-4 head lost two cylinders in its center, juxtaposed to the six-cylinder engines. The 2.5 engine also features five main bearings and eight overhead valves.

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 model year with the new XJ Cherokee. In 1986 the head went under a minor revision, the head bolts were increased from 7/16 to 1/2 inch. From 1997 to 2002 it was marketed as the "Power-Tech I4".^[3] It was produced through 2002 for the Jeep Wrangler, as well as for the Dodge Dakota pickup that also featured the AMC/Jeep designed four-cylinder as its standard engine from 1996 through 2002.

This lightweight engine is similar to its "big brother" 4.0 L, and although not powerful, it is durable with no reliability issues.^[4]

Output the final year was 121 hp (90 kW; 123 PS) 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; 114 PS) 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; 132 PS) and 149 lb·ft (202 N·m) of torque with 9.2:1 compression in the Cherokee and Comanche.^[5]

AMC 150/2.5	Compression	Horsepower	Torque
One-barrel carburetor	9.2:1	105 hp (78 kW; 106 PS) at 5,000	132 lb·ft (179 N·m) at 2,800
Throttle body injection (TBI)	9.2:1	117 hp (87 kW; 119 PS) at 5,000	135 lb·ft (183 N·m) at 3,500
Multi-point fuel injection (MPFI)	9.1:1	120 hp (89 kW; 122 PS) at 5,250	139 lb·ft (188 N·m) at 3,250

2.5 L AMC straight-4 in a 1992 Jeep YJ

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

Applications

The AMC 150/2.5 L 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

See also

• AMC straight-6 engine
• AMC V8 engine
• AMC Engines
• AMC/Jeep Transmissions
• List of Chrysler engines

External links

References

1. Ackerson, Robert C. (1991). The 50 year History of the Jeep. Motorbooks. ISBN 978-0-85429-533-3.
2. "Looking under the hood - Jeep power for AMC". Popular Mechanics 160 (4): 114, 153. October 1983. Retrieved 29 February 2012.
3. Lee, Christian (2007). High-Performance Jeep Wrangler TJ Builder's Guide. CarTech. p. 26. ISBN 978-1-932494-26-6. Retrieved 29 February 2012.
4. Zapp, Eric (2006). High-Performance Jeep Cherokee XJ Builder's Guide 1984-2001. CarTech. p. 99. ISBN 978-1-932494-14-3. Retrieved 29 February 2012.
5. Clark, Robert. "The AMC 2.5 liter four-cylinder engine". Allpar. Retrieved 29 February 2012.