AMC straight-4 engine

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AMC Straight-4 engine
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)
Cylinder block materialCast iron
Cylinder head materialCast iron
ValvetrainOHV 2 valves per cylinder
Compression ratio9.1–9.2:1
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 inline-four engine developed by American Motors Corporation (AMC) that was used in a variety of AMC, Jeep, and Dodge vehicles from 1984 to 2002.

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 the 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 and stroke of 3.875 in × 3.1875 in (98.43 mm × 80.96 mm) for an overall displacement of 150.36 cu in (2,464 cc). 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, when compared to the design for 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 for two reasons: the new AMC 2.5 replaced the four-cylinder engines that had been purchased from GM, and AMC continued to purchase 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) through 1986; when the 4.0 L was phased into production with the XJ models, 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 "PowerTech 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 as powerful, it is durable with no reliability issues.[6] The AMC 2.5 L is ranked among the very best of Jeep's I4 engines and is highly regarded for its robust build.[7]

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 CID 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 through 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.[8]

When emissions and fuel economy are a priority, the final MPFI versions of AMC's 2.5 L engine are considered superior.[7]

Fuel system Compression ratio Horsepower Torque
One-barrel carburetor (1984–1985) 9.2:1 105 hp (78 kW; 106 PS) at 5,000 rpm 132 lb⋅ft (179 N⋅m) at 2,800 rpm
Throttle body injection (TBI) (1986–1990) 9.2:1 117 hp (87 kW; 119 PS) at 5,000 rpm 135 lb⋅ft (183 N⋅m) at 3,500 rpm
Multi-point fuel injection (MPFI) (1991–2002) 9.1:1 120 hp (89 kW; 122 PS) at 5,250 rpm 139 lb⋅ft (188 N⋅m) at 3,250 rpm
2.5 L AMC straight-4 in a 1992 Jeep YJ
2.5 L AMC I-4 built in Kenosha, WI, on display

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


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

In China[edit]

AMC's Chinese joint venture Beijing Jeep Corporation also manufactured the 150 cubic-inch inline-four for installation in the locally built XJ Cherokee, originally called the Beijing Jeep BJ213 Cherokee. Local manufacture began in 1984 and the engine's name was C498QA in China.[9] A wide variety of variants and code names were applied to the Cherokee over the years, with the most drastic change being the facelifted Beijing Jeep 2500 which arrived in 2002. Beijing Jeep also developed a stroked 2.7 L version called the C498QA3, which entered production around 2003. This fuel-injected engine displaces 2,744 cc (167.4 cu in), produced 96 kW (131 PS; 129 hp) at 4800 rpm and was installed in a variant of the 2500 model called the Jeep 2700.[10]

From the beginning of the Jeep joint venture, Beijing had envisioned installing the C498QA engine in the original Beijing Jeep, with trial installation taking place in 1986 (the BJ 212 E model).[11] However, the first derivative of the old Beijing Jeep to be fitted with the American engine was the facelifted BJ 2020 V of 1999.[11] Beijing's BJ 752 prototype sedan was also fitted with the Jeep Cherokee engine, but only three examples were built in 1987 and 1988.[12] After the joint venture was dissolved in 2009, manufacture of the Cherokee continued under the Beijing Auto Works (BAW) name, although BAW only installed the C498QA engine in their Cherokee-based BJ2025 Leichi SUV from 2004 until 2008.[9]

See also[edit]

External links[edit]

Media related to AMC straight-4 engine at Wikimedia Commons

  • Hazel, Christian (4 January 2021). "2.5L or 4.0L? Engine Differences in Older Jeep Wranglers". Motor Trend. Retrieved 31 December 2022.


  1. ^ a b Ackerson, Robert C. (1991). The 50 year History of the Jeep. Motorbooks. ISBN 9780854295333.
  2. ^ a b "Looking under the hood - Jeep power for AMC". Popular Mechanics. Vol. 160, no. 4. October 1983. pp. 114, 153. Retrieved 31 December 2022 – via Google Books.
  3. ^ Ackerson, Robert C. (2005). Jeep CJ 1945-1986. Veloce. ISBN 9781904788966. Retrieved 31 December 2022 – via Google Books.
  4. ^ Lee, Christian (2007). High-Performance Jeep Wrangler TJ Builder's Guide. CarTech. p. 26. ISBN 9781932494266.
  5. ^ "1996 Dodge Trucks brochure". pp. 6, 7, 14. Retrieved 31 December 2022.
  6. ^ Zapp, Eric (2006). High-Performance Jeep Cherokee XJ Builder's Guide 1984-2001. CarTech. p. 99. ISBN 9781932494143.
  7. ^ a b Menon, Kiran (25 June 2021). "Jeep 2.5 Engine: Power & Reliability". Vehicle History. Retrieved 31 December 2022.
  8. ^ Clark, Robert (16 November 2020). "The AMC 2.5 liter four-cylinder engine". Retrieved 31 December 2022.
  9. ^ a b Cossard, Hubert (5 April 2013). "Chine - Moteur BJC C498QA I4 2.5 L 1983-2003". (in French). Archived from the original on 24 March 2020. Retrieved 31 December 2022.
  10. ^ Cossard, Hubert. "Chine - Moteur BJC C498QA3 I4 2.7 L 2003-2007". (in French). Archived from the original on 25 March 2020. Retrieved 31 December 2022.
  11. ^ a b van Ingen Schenau, Erik, ed. (2010) [2004], Cars and 4x4s from Beijing and Tianjin (Fourth ed.), Ortaffa, France: The China Motor Vehicle Documentation Centre, p. 93
  12. ^ van Ingen Schenau, p. 27