The AMC straight-6 engine is a family of straight-six engines produced by American Motors Corporation (AMC) and used in passenger cars and Jeep vehicles from 1964 through 2006. Production continued after Chrysler acquired AMC in 1987.
American Motors continued to use the Rambler straight-six engine initially designed by Nash Motors. It was redesigned as an OHV for the 1956 model year. This engine was discontinued in 1965.
American Motors introduced a completely new I6 design in 1964. This engine evolved in several displacements and underwent upgrades. Vehículos Automotores Mexicanos (VAM) also manufactured this family of six-cylinder engines, including two versions available only in Mexico.
A new 4.0 L engine was introduced by AMC in 1986 for the 1987 model year Jeep Cherokee (XJ) and became the final version of AMC's inline sixes. It is regarded as one of the best 4x4 and off-road engines. This engine was produced by Chrysler through 2006.
Among "classic American engines, the AMC straight-six stands as a testament to smart engineering and enduring performance".
Predecessors
The straight-six engine lineage at AMC goes back to Nash Motors. An economy-focused engine debuted in the 1941 Nash Ambassador 600 model. Its initial displacement of was subsequently increased to and finally to in 1952.
After Nash merged with Hudson to form AMC in 1954, efforts continued to enhance performance and meet evolving market demands. The engine's architecture underwent a significant transformation for the 1956 model year, transitioning from a flathead (L-head) side-valve configuration to an overhead valve (OHV) design. This modernization aimed to improve engine efficiency and power output. The flathead version was reintroduced in 1958, serving as the base economy engine for the newly launched Rambler American compact car. This dual-engine strategy persisted until 1965, catering to performance-oriented and economy-minded consumers.
To reduce vehicle weight and enhance fuel efficiency, AMC introduced a die-cast aluminum block version of the OHV engine in 1961. This innovative approach resulted in a significant weight reduction, with the aluminum engine weighing , compared to its cast-iron counterpart's . This aluminum engine was produced through 1964, showcasing AMC's engineering prowess and willingness to experiment with advanced materials.
While not known for high performance, this engine was known for reliability. This engine was also used in marine applications.
Modern Era
American Motors introduced a groundbreaking inline-six engine in 1964. It featured a short-stroke design and a robust seven-main bearing crankshaft with an overall design to provide good torque at low RPMs. This engine enjoyed a remarkable production run that continued under AMC and Vehículos Automotores Mexicanos (VAM) as well as by Chrysler until 2006.
Initially marketed as the "Torque Command" engine, the inline-six represented AMC's first genuinely modern six-cylinder engine. Road tests conducted by Consumer Reports lauded the engine as "a very smooth and quiet engine, which should give good performance."
To commemorate the engine's launch in May 1964, AMC produced 2,520 special "Typhoon" editions based on the Rambler Classic two-door hardtop. These distinctive vehicles featured the 8.5:1 compression ratio engine, a striking Solar Yellow exterior with a Classic Black roof, and "Typhoon" badging in place of the standard "Classic" script. Notably, all other Rambler Classic options, except alternative engine choices, were available on the Typhoon edition.
For the 1965 model year, the 232 engine superseded the aging Nash OHV inline-six in the Classic and Ambassador models. This marked the return of a six-cylinder engine in the Ambassador line since 1956, reflecting AMC's commitment to offering a wider range of powertrain options.
In 1966, AMC expanded its six-cylinder lineup by introducing the version of the 232 engine. This smaller variant replaced the OHV and L-head engines across AMC's passenger car lineup.
Both the 199 and 232 engines shared a bore, differing only in stroke: for the 199 and for the 232. The 199 engine was discontinued in 1970, while the 232 continued production alongside the larger engine, which the increase in displacement was achieved by employing a stroke crankshaft and a slightly taller engine block.
More stringent emission control regulations, coupled with the growing weight of vehicles due to safety mandates, led to a gradual decline in engine power output, ultimately resulting in the discontinuation of the 232 in 1979.
199 The engine was produced from 1965 through 1970. Rated at at 4400 rpm and of torque at 1600 rpm, it was the standard engine beginning with the compact 1966 Rambler American series.
Navarro Indy Barney Navarro selected the 199 AMC engine to power a race car for the Indianapolis 500. Navarro had previously applied turbocharging to a variety of engines that led to the 199 engine's Indy-related application "based on a Stone-Age-strong Nash 6."
This engine had not been used in an IndyCar. However, Navarro selected it "due both to its strong bottom end and thick cylinder walls." For the first Indy attempt, Navarro designed a fuel-injection system, a unique head, and a single turbo to achieve at 6000 rpm. This was with the stock block featuring seven main bearings and large journal sizes, while the second block was drilled for four-bolt caps. Successive engines incorporated double turbochargers to produce .
Navarro fielded a 1964 Watson car with the AMC 199 engine for three years at the Indianapolis 500. However, the #50 Navarro-Rambler never qualified due to problems with drivers and with the suspension of the cars. The car was also entered at the 1971 IndyCar "Rafaela 300" season opener in Argentina. This was the car's fourth actual race start, and it began at 19 on the starting grid. Dave Strickland drove it for 45 laps. This car was then driven by Les Scott in practice for the 1971 Indy 500 race. The following year, another attempt to qualify was with Leon Sirois as the driver.
An auction was held on 14 July 2005, to clear the remaining contents of the Navarro Engineering shop in Los Angeles. A private collector purchased a complete Navarro engine for $15,000.
Rambler Classic (1965–1966, fleet cars only) Rambler American/AMC Rambler (1965–1969) AMC Hornet (1970) AMC Gremlin (1970) VAM Rambler American (mid 1965–1969) U.S. equivalent — AMC Rambler American and AMC Rambler sedans VAM Camioneta Rambler American (mid 1965–1967) U.S. equivalent — AMC Rambler American wagon
232 The engine was produced from 1964 until 1979. The 232 was the base six-cylinder engine on many models through 1979, and even towards the end of its usage, it was considered reasonably modern in design.
After its midyear 1964 introduction in the "Typhoon" two-door hardtop as part of the mid-sized Rambler Classic line, the 232 engine was adapted to fit into the smaller 1965 Rambler American by using a special short water pump, an adaptive piece also used in the 1971 through 1975 Jeep CJ-5. Air conditioning was available only with the older 196 engine in the American models because there was not enough space for the compressor with the longer 232.
Through the 1970 model year, the 232 shared a deck height with the engines. Starting in 1971, AMC raised the deck height to produce the 258, and the 232 adopted the 199's longer connecting rods and shared deck height with the 258. Bore and stroke remained the same.
In 1972, the bell housing bolt pattern changed to match the larger version used on the V8 engines.
Changes for the 1976 model year included fuel economy improvements that reduced emissions and warmup time. This was accomplished by reshaped carburetor air passages that pushed the fuel efficiency of a 232-equipped AMC Gremlin to as tested by the United States Environmental Protection Agency, compared to in 1975.
Rambler Classic (1964–1966) Rambler American/AMC Rambler (1964–1969) Rambler/AMC Marlin (1965–1967) Rambler/AMC Ambassador (1965–1970) Rambler/AMC Rebel (1967–1970) AMC Javelin (1968–1974) AMC Hornet (1970–1977) AMC Gremlin (1970–1978) AMC Matador (1971–1974) AMC Pacer (1975–1979) AMC Concord (1978–1979) AMC Spirit (1979) Jeep CJ (1972–1979) Jeep Cherokee (1974–1979) Jeep Wagoneer (1965–1971) Jeep J-Series (1965–1970) Jeep Commando (1972–1973) (1976 in Spain) International Scout (1969–1971) International Light Line pickups/Travelall (1968–1971) VAM Rambler American Hardtop (1965) U.S. equivalent AMC Rambler American 440H hardtop VAM Rambler American Rally (1969–1971) U.S. equivalent 1969 AMC Rambler Rogue sedan instead of hardtop and 1970–1971 Hornet X VAM Rambler American (1968–1972) U.S. equivalent AMC Rambler American sedans and AMC Hornet sedans VAM Camioneta Rambler American (1968–1972) U.S. equivalent AMC Rambler American wagon and AMC Hornet Sportabout VAM Rambler Classic 660 (1965) U.S. equivalent AMC Rambler Classic VAM Rambler Classic 770 (1966–1969) U.S. equivalent 1966 AMC Rambler Classic sedans plus AMC Rebel four door sedan VAM Rambler Classic SST (1967–1969) U.S. equivalent AMC Rebel hardtop VAM Javelin (1968–1969) U.S. equivalent AMC Javelin VAM Gremlin (1974–1976) U.S. equivalent AMC Gremlin
252 The engine was produced by AMC's Mexican subsidiary Vehículos Automotores Mexicanos (VAM) beginning in 1969 and was dropped after 1972, replaced with AMC's 258 for the 1973 model year onward. This was similar to a 232 in stroke with a larger bore, for an actual displacement of . It was produced in VAM's Lerma, Estado de México engine plant.
Output for 1972 Rambler American Rally model (gross): Horsepower at 4600 rpm Torque at 2300 rpm
Engine dimensions: Compression ratio 9.5:1 Intake valve diameter Exhaust valve diameter Connecting Rod length Deck height Bore Stroke
VAM Javelin (1969–1970) U.S. equivalent — AMC Javelin VAM Rambler Classic SST (1969–1971) U.S. equivalent — AMC Rebel hardtop and AMC Matador hardtop VAM Rambler Classic 770 (1970) U.S. equivalent — AMC Rebel sedan VAM Rambler Classic DPL (1971) U.S. equivalent — AMC Matador sedan VAM Rambler American Rally (1972) U.S. equivalent — AMC Hornet Rallye X
258
The was produced from 1971 through 1990. It featured an undersquare bore and stroke; it was otherwise similar to the 199 and 232 (Note: Starting in the mid-1970s the 258's bore and stroke was changed to a bore over a 3.75" stroke. This allowed one block to be used for both the 232 and 258 and the same crankshaft blank could be milled to the two different strokes).
This engine is considered reliable, inexpensive, and torquey. Later 258 models (starting with the 1980 model year for California AMC Concords and Spirits, 1981 for California Jeeps, California Eagles, and 49-state Concord and Spirits, as well as in 1982 for 49-state Eagles and all other applications) are equipped with AMC Computerized Engine Control (CEC) system. For 1981, as part of a weight reduction program (aluminum intake manifold, plastic rocker arm cover), the crankshaft was changed from a twelve counterweight design to four, saving approximately .
This engine also found use in farm/industrial applications such as the International Harvester 4000 swather.
AMC Hornet/Concord/Eagle (1971–1988) AMC Pacer (1975–1980) AMC Matador (1971–1978) AMC Gremlin and Spirit (1971–1983) International Scout and Light Line trucks (1972–1980) Jeep CJ (1972–1986) Jeep Cherokee and Wagoneer (1972–1986) Jeep J-Series (1971–1988) Jeep Wrangler (1987–1990) Jeep Commando (1972–1973) VAM Rambler American (1973–1974) U.S. equivalent — AMC Hornet sedans VAM Rambler American Rally (1973–1974) U.S. equivalent — AMC Hornet X sedan instead of a hatchback VAM Camioneta Rambler American (1973–1974) U.S. equivalent — AMC Hornet Sportabout VAM American (1975–1983) U.S. equivalent — AMC Hornet sedan base model and AMC Concord sedan base model