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 | |
| 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.
American Motors devoted three years to the development of a new four-cylinder engine. The brand new engine was designed to use AMC's existing spacing between the cylinder bores so that the tooling remained the same. 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.
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."
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 2.5L also shared an 18mm threaded oil filter used with the GM 2.8L (ACDelco PF47 or equivalent) to 1986; when the 4.0L was phased into production with the XJ the oil filter was changed over to a 20mm thread size shared with Renaults until 1991.
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