AMC Straight-4 engine
Encyclopedia
The American Motors Corporation straight-4
engine was used by a number of AMC, Jeep
, and Dodge vehicles from 1984-2002.
, "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."
bored to 3.875 in (98.4 mm) and de-stroked to 3.1875 in (81 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 at 5400 rpm and 145 lb·ft of torque at 3250 rpm using sequential multiple-port fuel injection
(MPFI). For comparison, the 258 I6 provided 112 hp at 3200 RPM and 210 lb·ft 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 and 149 lb·ft of torque with 9.2:1 compression in the Cherokee and Comanche.
Note that the TBI system was made by Renix
and used from mid-1986-August 1990.
Straight-4
The inline-four engine or straight-four engine is an internal combustion engine with all four cylinders mounted in a straight line, or plane along the crankcase. The single bank of cylinders may be oriented in either a vertical or an inclined plane with all the pistons driving a common crankshaft....
engine was used by a number of AMC, Jeep
Jeep
Jeep is an automobile marque of Chrysler . The first Willys Jeeps were produced in 1941 with the first civilian models in 1945, making it the oldest off-road vehicle and sport utility vehicle brand. It inspired a number of other light utility vehicles, such as the Land Rover which is the second...
, and Dodge vehicles from 1984-2002.
- 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 LunnRoy Lunn
Roy Lunn is an engineer in the automotive industry. He has forty-one years in the design development and production of vehicles and most notably served as the head of engineering at American Motors Corporation from 1971 to 1987....
, "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
AMC Eagle
The AMC Eagle is a compact-sized four-wheel drive passenger vehicle that was produced by American Motors Corporation . The AMC Eagle line of vehicles inaugurated a new product category of "sport-utility" or crossover SUV....
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."
The AMC 150/2.5 L engine
The 2.5 L inline-4 was a shortened version of the 258 6-cylinder engineAMC Straight-6 engine
The American Motors Corporation straight-6 family of engines was used by a number of AMC and Jeep vehicles from 1964 through 2006.-195.6:American Motors' first straight-six engine was the...
bored to 3.875 in (98.4 mm) and de-stroked to 3.1875 in (81 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
Combustion chamber
A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the 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
Bell housing
"Bell housing" is a colloquial/slang term for the portion of the transmission that covers the flywheel and the clutch or torque converter of the transmission on vehicles powered by internal combustion engines. This housing is bolted to the engine block and derives its name from the bell-like...
bolt pattern, AMC/Jeep engineers adopted the General Motors
General Motors
General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
small V6 and four-cylinder bolt pattern (commonly used with GM's transverse-mounted powerplants
Transverse engine
A transverse engine is an engine mounted in a vehicle so that the engine's crankshaft axis is perpendicular to the long axis of the vehicle. Many modern front wheel drive vehicles use this engine mounting configuration...
) 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
Jeep Cherokee (XJ)
The Jeep Cherokee is a unibody compact SUV. It shared the name of the original full-size SJ model, but without a body-on-frame chassis, it set the stage for the modern SUV. Its innovative appearance and sales popularity spawned important imitators as other automakers began to notice that this...
. It was produced through 2002 for the Jeep Wrangler
Jeep Wrangler
The Jeep Wrangler is a subcompact four-wheel drive sport utility vehicle and an off-road vehicle manufactured by American automaker Chrysler, under its Jeep marque – and now in its fourth generation. It is a successor to the famous World War II 'Jeep' vehicle by way of the Willys civilian...
, as well as for the Dodge Dakota
Dodge Dakota
The Dodge Dakota is a mid-size pickup truck from Chrysler's Ram division. From its introduction through 2009, it was marketed by Dodge. The first Dakota was introduced in 1986 as a 1987 model alongside the redesigned Dodge Ram 50...
pickup that also used the AMC/Jeep designed four since 1996.
| AMC 150/2.5 | Specifications |
| Bore x Stroke | 3.875 in (98.4 mm) x 3.1875 in (81 mm) |
| Displacement Engine displacement Engine displacement is the volume swept by all the pistons inside the cylinders of an internal combustion engine in a single movement from top dead centre to bottom dead centre . It is commonly specified in cubic centimeters , litres , or cubic inches... |
150.4 CID (2,464 cc) |
| Valvetrain Valvetrain Valvetrain is an all-encompassing term used to describe the mechanisms and parts which control the operation of the valves. A traditional reciprocating internal combustion engine uses valves to control air and fuel flow into and out of the cylinders, facilitating combustion.-Layout:Valvetrain: The... |
eight valves (overhead) |
| Main bearing Main bearing In a piston engine, the main bearings are the bearings on which the crankshaft rotates, usually plain or journal bearings.All engines have a minimum of two main bearings, one at each end of the crankshaft, and they may have as many as one more than the number of crank pins... s |
five |
| Compression ratio Compression ratio The 'compression ratio' of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity... |
9.1:1 to 9.2:1 depending on year |
Output the final year was 121 hp at 5400 rpm and 145 lb·ft of torque at 3250 rpm using sequential multiple-port fuel injection
Fuel injection
Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....
(MPFI). For comparison, the 258 I6 provided 112 hp at 3200 RPM and 210 lb·ft of torque at 2000 rpm in its final year with the computer-controlled carburetor
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....
.
For several years, the engine was detuned for the Wrangler; from at least 1992-1995, it produced 130 hp and 149 lb·ft of torque with 9.2:1 compression in the Cherokee and Comanche.
| AMC 150/2.5 | Compression | Horsepower | Torque |
| One-barrel carburetor Carburetor A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom.... |
9.2:1 | 105 hp at 5,000 | 132 lb·ft at 2,800 |
| Throttle body injection (TBI) | 9.2:1 | 117 hp at 5,000 | 135 lb·ft at 3,500 |
| Multi-point fuel injection (MPFI) | 9.1:1 | 120 hp at 5,250 | 139 lb·ft at 3,250 |
Note that the TBI system was made by Renix
Renix
Renix made automobile electronic ignitions, fuel injection systems, electronic automatic transmission controls, and various engine sensors.The term Renix also has a number of applications...
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 EagleAMC EagleThe AMC Eagle is a compact-sized four-wheel drive passenger vehicle that was produced by American Motors Corporation . The AMC Eagle line of vehicles inaugurated a new product category of "sport-utility" or crossover SUV....
- 1984–2000 Jeep Cherokee (XJ)Jeep Cherokee (XJ)The Jeep Cherokee is a unibody compact SUV. It shared the name of the original full-size SJ model, but without a body-on-frame chassis, it set the stage for the modern SUV. Its innovative appearance and sales popularity spawned important imitators as other automakers began to notice that this...
- 1986–1992 Jeep ComancheJeep ComancheThe Jeep Comanche is a pickup truck version of the Cherokee compact SUV that was produced from 1985 to 1992. Rear wheel and four-wheel drive models were available, as well as two cargo box lengths of six-feet or seven-feet .-Introduction:During the mid-1980s, according to AMC Chairman W...
(MJ) - 1987–2002 Jeep WranglerJeep WranglerThe Jeep Wrangler is a subcompact four-wheel drive sport utility vehicle and an off-road vehicle manufactured by American automaker Chrysler, under its Jeep marque – and now in its fourth generation. It is a successor to the famous World War II 'Jeep' vehicle by way of the Willys civilian...
(YJ/TJ) - 1988–1989 Eagle PremierEagle PremierThe Eagle Premier was a full-size automobile developed by the American Motors Corporation and Renault partnership, inherited by Chrysler Corporation when it acquired AMC in 1987, and marketed from 1987 through 1992...
- 1996–2002 Dodge DakotaDodge DakotaThe Dodge Dakota is a mid-size pickup truck from Chrysler's Ram division. From its introduction through 2009, it was marketed by Dodge. The first Dakota was introduced in 1986 as a 1987 model alongside the redesigned Dodge Ram 50...
See also
- AMC Straight-6 engineAMC Straight-6 engineThe American Motors Corporation straight-6 family of engines was used by a number of AMC and Jeep vehicles from 1964 through 2006.-195.6:American Motors' first straight-six engine was the...
- AMC V8 engineAMC V8 engineAmerican Motors Corporation produced a series of widely-used V8 engines from the mid-1950s before being absorbed into Chrysler in 1987. Chrysler kept the AMC V8 in production until 1991 for the Jeep Grand Wagoneer....
- AMC EnginesAMC EnginesThe American Motors Corporation used V8, straight-6, V6, and straight-4 engines in various passenger automobiles and Jeep vehicles from 1954 through 2006. Some engines were of AMC design or inherited from its constituents...
- AMC/Jeep Transmissions
- List of Chrysler engines