AMC straight-4 engine

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AMC straight-4 engine
Jeep 2.5 liter 4-cylinder engine chromed a.jpg
2.5 L AMC straight-4 with MPFI
Also calledPowerTech
Displacement150.4 cu in (2.5 L)
Cylinder bore3.875 in (98.4 mm)
Piston stroke3.1875 in (80.96 mm)
Block materialCast iron
Head materialCast iron
ValvetrainOHV 2 valves per cylinder
Compression ratio9.1:1-9.2:1
Fuel system
Fuel typeGasoline
Oil systemWet sump
Cooling systemWater-cooled
Power output105–130 hp (106–132 PS; 78–97 kW)
Torque output132–150 lb⋅ft (179–203 N⋅m)
SuccessorChrysler 1.8, 2.0 & 2.4 engine

The AMC straight-4 engine is a 2.5 L straight-4 engine developed by American Motors Corporation (AMC) that was used in a variety of AMC, Jeep, and Dodge vehicles from 1984 to 2002.

Note: Although the GM Iron Duke was a predecessor I4 engine in some AMC vehicles, it shares nothing in common with the AMC 2.5 L.


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 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."[3] Although some of components were interchangeable between the AMC 258 cu in (4.2 L) 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]


The AMC 150 cu in (2.5 L) engine has a bore x stroke of 3.875 in × 3.1875 in (98.43 mm × 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, opposed 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 2.5 L also shared an 18mm threaded oil filter used with the GM 2.8 L (ACDelco PF47 or equivalent) to 1986; when the 4.0 L was phased into production with the XJ the oil filter was changed over to a 20mm thread size shared with Renaults until 1991.

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".[4] 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 on regular cab rear-wheel drive models from 1996 through 2002.[5]

This lightweight engine is similar to its "big brother" 4.0 L, and although not powerful, it is durable with no reliability issues.[6]

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 ratio in the Cherokee and Comanche.[7]

AMC 150 cu in (2.5 L) Compression ratio Horsepower Torque
One-barrel carburetor (84-85) 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) (86-90) 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) (91-02) 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.


The AMC 150 cu in (2.5 L) engine was used in the following vehicles:

See also[edit]

External links[edit]

Media related to AMC straight-4 engine at Wikimedia Commons


  1. ^ a b Ackerson, Robert C. (1991). The 50 year History of the Jeep. Motorbooks. ISBN 978-0-85429-533-3.
  2. ^ a b "Looking under the hood - Jeep power for AMC". Popular Mechanics. 160 (4): 114, 153. October 1983. Retrieved 29 February 2012.
  3. ^ Ackerson, Robert C. (2005). Jeep CJ 1945-1986. Veloce. ISBN 9781904788966. Retrieved 4 November 2019.
  4. ^ Lee, Christian (2007). High-Performance Jeep Wrangler TJ Builder's Guide. CarTech. p. 26. ISBN 978-1-932494-26-6. Retrieved 29 February 2012.
  5. ^ "1996 Dodge Truck Brochure". Old Car Brochures. pp. 6, 7, 14. Retrieved 4 November 2019.
  6. ^ 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.
  7. ^ Clark, Robert. "The AMC 2.5 liter four-cylinder engine". Allpar. Retrieved 29 February 2012.