This was AMC's first V8 engine designed and manufactured from '56 to '67. It never wore a 'Nash' or 'Hudson' label on its valve cover. The engine was traditionally called 'Rambler V8' because it powered those cars AMC made during the American Manufacturer Association ban on factory supported racing from 1957 to 1962, whereas the former racing goals of Nash and Hudson motorcars were ended and those two names were permanently retired.
The rather specious traditional tale of how AMC's first V8 engine came into being is as follows;
American Motors' president, George W. Mason, negotiated a verbal agreement with Packard that the two companies would supply parts for each other when practical. This was a prelude to a possible merger of the two companies at a later date, but that never occurred. With the industry-wide acceptance of V8 engine designs after World War II, AMC started buying Packard V8s in 1954 for the 1955 Nash Ambassador and Hudson Hornet. These were supplied with Packard "Ultramatic" automatic transmissions - exclusively. Packard sent AMC some parts bids, but these were rejected as too expensive. George W. Romney, AMC's new head, decided against further relationships with Packard shortly after entering the position of CEO in October 1954 after Mason's sudden death.
Romney ordered his engineering department to develop an in-house V8 as soon as possible. The engineering department hired David Potter, a former Kaiser Motors engineer, to help develop the engine. Potter had previously worked on a V8 design for Kaiser, and they were able to get the all new V8 into production in less than 18 months, an extraordinary engineering feat at the time considering using slide rules was the norm.
The 1956 SAE article named "The New American Motors V8" tells the otherwise true story of who, what, where and why.
All these engines share common external dimensions, light weight - about 600 lb (270 kg) - forged crankshaft and rods, as well as most other parts. The stroke for all Gen-1 V8s is 3.25 inches (82.6 millimetres). Engine displacement was a factor of the bore: the 250 cu in (4.1 L) has a 3.5-inch (88.9 mm) bore, 287 cu in (4.7 L) 3.75 in (95.3 mm), and the 327 cu in (5.4 L) a 4.0 in (101.6 mm) bore. The bore size is cast on the top of the block near the back of the right bank cylinder head. Like most V8 engine designs of the 1950s, the block features a deep skirt where the casting extends below the crankshaft centerline, forming a very rigid crankcase gallery. The oil system feeds a central gallery to the cam and crankshaft first from front to rear, and then dividing at the front to feed the two lifter galleries from front to rear. From the rear of the two lifter galleries oil is then supplied up to the two rocker arm shafts which serve as galleries to lubricate the valve train. The fore and aft direction changes are designed to eliminate stale oil areas which tend to form sludge deposits. Juxtaposed with the Rambler V8, the Chevrolet small-block engine feeds both lifter galleries and the central cam and crankshaft galleries simultaneously through a three way split from the rear, having oil proceed to the front of the engine, the lifter galleries feeding oil to the valve train through hollow pushrods.
American Motors' first V8 in-house engine, the 250, was used in American Motors Corporation automobiles from 1956 through 1961. It was a modern OHV/pushrod engine design and made its debut in the Nash Ambassador and Hudson Hornet "Specials" of 1956. These cars had the top-of-the-line model trim, but were built on the shorter wheelbase (Statesman and Wasp) models (hence the "Special" name). The 250 uses solid lifters and came in two- and four-barrel carburetor varieties (4V only in Nash/Hudson "Specials").
The 250 V8 was optional in the 1957 Rambler. All 1958-60 V8 Ramblers were called "Rebels" and designated as a different series. It is easy to confuse the 1957 Rambler V8 and the 1958-'60 Rebel line with the special 1957 Rambler Rebel, a limited edition muscle car (see 327 below). In 1961, The Rambler Six was renamed the "Rambler Classic" to avoid model confusion in the Rambler line-up. A V8 engine then became an option in the Classic instead of a separate model.
In mid-model year 1963, AMC introduced a 287 cu in (4.7 L) V8. When the 250 was dropped in 1961, there was no V8 option for Rambler models other than the top of the line Ambassador, which was only available with the 327. Dealers complained, so the 287 was introduced as an option for the "mid-size" Rambler. Like the 327, it uses hydraulic valve lifters. Only two-barrel models were produced, there were no four-barrel options from the factory for the 287 as this was the economy model V8. The 287 engine was produced through the 1966 model year.
The AMC 327 is similar to the 287, but displaces 327 cu in (5.4 L) due to the bore increase to 4.0 inches (102 mm). Unlike the 250, the 327 was produced with hydraulic valve lifters. Contrary to some myths, the AMC V8 was not built by Chevrolet, whose own 327 V8 later became better known. The AMC 327 was introduced five years before the Chevrolet 327 engine was manufactured.
The AMC 327 engine debuted in a special edition Rambler Rebel, of which 1,500 were made. They were an early American muscle car. All Rebels had silver paint with a gold-anodized "spear" on each side. The 327 was not available in any other Rambler models in 1957 other than the special edition Rebel. The Rebel's engine differs from the 327s installed in the 1957 Nash Ambassador and Hudson Hornet models in that it uses mechanical valve lifters and a higher compression ratio. Since both engines were rated at 255 hp (190 kW; 259 PS), it is probable that the Rebel's was underrated.
The Nash Ambassador and Hudson Hornet "Special" models were dropped after 1957, replaced by the 1958 Rambler Rebel with the 250 V8. The Rebel was a Rambler with a V-8 (and necessary mods such as stronger front springs and rear axle). The Rebel name was added to differentiate the standard six-cylinder Rambler from the V-8 model. The big Nash and Hudson cars were also dropped after 1957, replaced by the 1958 "Ambassador by Rambler" — a stretched Rebel with the 327 V8 instead of the 250. The 327 was exclusive to the Ambassador line and could not be ordered in a Rebel (or later Classic) through 1964. For 1965 and 1966 the 287 and 327 were both available in the Classic and Ambassador.
The 327, with two barrel carburetor only, was sold to Kaiser-Jeep from 1965 to 1967 for use in the Jeep Wagoneer SUV and Gladiator pick-up truck. Jeep named it the "Vigilante" V8. Kaiser-Jeep switched to the Buick 350 in 1967 after AMC discontinued the 327. The Buick V8 engine option continued through 1971 after which Jeeps returned to AMC V8 engines, American Motors having purchased Jeep from Kaiser in 1970.
There were low- and high-compression versions of the 327 starting in 1960. Prior to 1960 all 327s were high compression. All low compression models used a two-barrel carburetor and all high-compression models received a four-barrel carb. Low-compression is 8.7:1, high 9.7:1, effected by a difference in pistons.
The 327 was also offered as a marine engine as the "Fireball" by Gray Marine Motor Company.
The AMC 327 was to be the first commercial electronic fuel injected (EFI) "Electrojector" production engine. Press reports about the Bendix-developed system in December 1956 were followed in March 1957 by an AMC price bulletin offering the EFI option on the Rambler Rebel for US$395, but due to supplier difficulties, fuel-injected Rebels were only available after June 15. Teething problems with the Electrojector unit meant that only a few engineering and press cars were built, estimated to be no more than six units. At least two pre-production Rebels with EFI, however, are known to have been built. One was sent to Daytona Beach, Florida for "Speed Week" (the forerunner of today's Daytona 500). It was the second fastest car on the beach, bested only by a 1957 Chevrolet Corvette with mechanical fuel injection, and only by a couple tenths of a second.
The EFI 327 was rated at 288 hp (215 kW; 292 PS) and the regular four-barrel carbureted model at 255 hp (190 kW; 259 PS). The EFI system in the Rebel was a far more-advanced setup than the mechanical types then appearing on the market and the engines ran fine in warm weather, but suffered hard starting in cooler temperatures. All the EFI cars were reportedly converted to four-barrel carbs before being sold; none are known to have existed outside the engineering department at AMC.
The main problem was that early electronics were not fast enough for "on the fly" engine controls. This setup was utilised by Chrysler for the 1958 model year on its Dodge, Chrysler, Plymouth, and DeSoto carlines. It too failed, having the same problems.
Bendix licensed patents based on their 1950s design (patent dated 1960) to Bosch, who perfected it as the basis for their D-Jetronic, et seq. injections system, first used in 1967.
The 250 and 327 were also offered as a marine engine known as the "Fireball" by Gray Marine Motor Company starting in 1958. Gray started offering the 250 in 1959. The 250 was offered in 135, 160, 170, 175, 178 and 185 horsepower versions. The 327 was made in 188, 215, 220, 225 and 238 horsepower levels. Gray used the 250 through 1966. The 327 was used as a 220 hp model in 1967, the last year an AMC V-8 was used.
The new-generation AMC V8 was first introduced in 1966. It is sometimes referred to as the "Gen-2" AMC V8. The first version was the completely new 290 cu in (4.8 L) "Typhoon" V8 introduced in a special mid-1966 model year "Rogue" hardtop. Available in 200 hp (149 kW; 203 PS) two-barrel carburetor version or producing 225 hp (168 kW; 228 PS) with a four-barrel carburetor and high compression, the new engines utilized "thin-wall" casting technology and weighed only 540 pounds (245 kg).
All three engine sizes - 290 cu in (4.8 L), 343 cu in (5.6 L), and 390 cu in (6.4 L) - share the same basic block design—the different displacements are achieved through various bore and stroke combinations. All blocks share the same external measurements and thus can be swapped easily.
Bore center measurement was kept the same as the Gen-1 V8 at 4.75 in (120.7 mm) so that boring equipment could be reused. Other than that, this engine is vastly different from the Gen-1 model. The Gen-1 engine is physically the size of a big-block Ford or GM engine, and is sometimes called a "big-block". The Gen-2 is closer to the physical size of U.S. made small-block V8s except for the bore centers, which are the same as some big-block engines. There are no shared parts between the AMC Gen-1 and Gen-2/3 engines.
Contrary to a popular myth, the AMC V8 was not built by Ford or anyone else although it bears an uncanny resemblance to the later Buick V8 engines (400, 430, 455). It shares the same design employing a timing gear case that mounts both distributor and oil pump. It also shares the same oiling scheme employing a single passage to feed both cam and crank from the right lifter bank by tangentially intersecting the cam bore instead of two drilled passages, one from the cam to crank and another from the crank to the right lifter bank. Some electrical parts (starter and distributor) were shared with Fords, and some models used Motorcraft (Ford) carburetors, but the balance of the engine design is unique.
The Gen-2 AMC V8 was first introduced at 290 cu in (4.8 L) in 1966. It was used exclusively in the Rambler American model the first year. The 343 cu in (5.6 L) came out in 1967 and the AMX 390 cu in (6.4 L) arrived in mid-1968. These engine blocks were unchanged through the 1969 model year.
The head used during this time was the so-called "rectangle port", named after its exhaust port shape. The 290 heads use smaller valves, 1.787 in (45.4 mm) intake and 1.406 in (35.7 mm) exhaust, in order to prevent problems with the small bore. The 343 and the AMX 390 use the same larger valve heads, 2.025 in (51.4 mm) intake and 1.625 in (41.3 mm) exhaust.
From 1976 to 1979, Jerry Grant "drove the most powerful car ever to appear in Indy car racing" - a turbocharged 209 cu in (3.4 L) stock two-valve AMC Gen-2 block V8 engine producing 1,100 hp (820 kW; 1,115 PS) in his Eagle 74 chassis. The car was fast on the straightways, but the engine's weight made corners more difficult to handle.
The base 289.92 cu in (4.8 L) 290 produces 200 or 225 hp (149 or 168 kW) with a two-barrel or four-barrel carburetor, respectively. It was built from the mid-1966 model year through the 1969 model year. It has a 3.75 in (95.3 mm) bore and 3.28 in (83.3 mm) stroke. Only 623 cars were built in 1966 with the 290 engine. These engines were available in special Rambler American two-door Rogue models. The newly powered Rogue was available with either a three-speed automatic or a floor mounted four-speed manual transmission, and made the car "suitable for the Stoplight Grand Prix."
The 342.88 cu in (5.6 L) 343 has a 4.08 in (103.6 mm) bore and 3.28 in (83.3 mm) stroke. The basic 343/2V produced 235 hp (175 kW; 238 PS) and was built from 1967 through 1969. Output for the optional four-barrel carburetor version is 280 hp (209 kW; 284 PS) and produces 365 pound force-feet (494.9 N·m) of torque (gross). This version has a 10.2:1 compression ratio.
In addition to the largest bore and stroke, the 389.55 cu in (6.4 L) AMX 390 motor also received heavier main bearing support webbing and a forged steel crankshaft and connecting rods. Forged cranks and rods were used for their known strength—there was inadequate time for testing cast parts for durability without delaying AMC's introduction schedule. Once forging dies were made it was not cost effective to test cast parts due to the relatively low number of engines produced. The use of these stronger components was also continued with the production of 401 engines. This is an advantage of these AMC engines when used in heavy-duty and high-performance applications because they have no problems with their rods breaking; unlike other domestic automakers' large displacement small block engines. The Gen-2 AMX 390 produces 315 hp (235 kW; 319 PS) and was built in 1968 and 1969. Bore is 4.165 in (105.8 mm) and the stroke is 3.574 in (90.8 mm). Maximum factory recommended overbore is only 0.020 in (0.508 mm), although they are commonly bored 0.030 in (0.8 mm). In 1970, AMC changed the head to the "dog-leg" exhaust port design.
In 1970, all three blocks grew in deck height and gained a new head design. These changes made this the third generation of AMC V8, hence it is sometimes referred to as the "Gen-3" AMC V8. The stroke and deck height on the 290 and 343 was increased by 0.16 in (4.06 mm) on both engines, becoming the 304 cu in (5.0 L) and 360 cu in (5.9 L), respectively. The 1970 AMX 390 remained at the same displacement by using a special rod and piston for this year only. It is believed that AMC kept the 390 this last year due to the reputation it had garnered in the two seater AMX, which was discontinued after 1970. In 1971 the 390 was also stroked by 0.16 in (4.06 mm) to become the 401 engine.
The other change in 1970 was the switch to the "dog-leg" heads. These heads flow 20% better on the exhaust side than the 1966-'69 rectangle port heads and are thus the best for performance. There are two reasons for the flow increase: First, the area of the port is larger, due to the dog leg. Second, the shape of the port floor was changed from a concave to a convex curve. The concave floor tended to bend the exhaust flow upwards which caused turbulence when the flow was forced to go down into the exhaust manifolds. By switching to a convex floor the curvature of the flow starts in the head and proceeds much more smoothly into the exhaust manifold resulting in less turbulence and better flow.
The center two intake bolts on each head were relocated to prevent accidental mix-ups of Gen-2 and Gen-3 intakes. The intakes can be interchanged by slotting the bolt holes, but the added deck height of the GEN-3 engine means that sealing and port match will be compromised. Gen-3 intakes can be machined to fit Gen-2 engines by surface grinding the intake flanges and slotting the center holes.
There is a persistent myth about 1970-mid 1971 319 and 291 AMC heads. These heads have the dog-leg exhaust ports and 50-52 cc combustion chambers. They are commonly identified by the first three (319) or last three (291 for the 360-401 heads; 304 used a different casting) digits of the casting number. There was a U.S. auto industry-wide shift to lower compression ratios in mid 1971, so AMC increased combustion chamber size to 58-59 cc. The first three digits of the casting number on the large chamber heads are 321, 322, or 323 depending on year. The only difference between small and large chamber Gen-3 heads is the combustion chamber size. The early heads are not "the best" AMC heads as many have come to believe. They will raise compression on a later engine with no other changes, but if building an engine get the proper pistons for the desired ratio. There is no reason to search out these relatively hard to find, and more expensive when found, heads for performance, except for the fact they are a factory-reliable high-compression performance part which is generally viewed as more valuable and instantly desirable.
The 304 has a displacement of 303.73 CID (4,977.2 cc) which produced 210 hp (157 kW; 213 PS) in 1970-71 and was built starting in 1970. Later models produced less power from the factory, going down yearly. 1972-78 models were rated at 150 hp (112 kW; 152 PS). It was rated at 130.5 hp (97 kW; 132 PS) in 1979, the last year it was installed in passenger cars, and 125 hp (93 kW; 127 PS) in 1980-81, the last years it was used in Jeep vehicles.
The AMC 360 has a displacement of 359.21 CID (5,886.3 cc). The 2-barrel produced 235 hp (175 kW; 238 PS) to 245 hp (183 kW; 248 PS) in 1970 to early 1971 while the 4-barrel produced 285 hp (213 kW; 289 PS) to 295 hp (220 kW; 299 PS), 175 hp (130 kW; 177 PS) to 220 hp (164 kW; 223 PS) from mid-1971 to 1975, 140 hp (104 kW; 142 PS) to 180 hp (134 kW; 182 PS) in 1976, 129 hp (96 kW; 131 PS) in 1977, and 160 hp (119 kW; 162 PS) from 1978 to 1991.
This engine was used in the 1970 AMX as the base engine and also in the 1970 Rebel, 1971-1978 Matador, Jeep J-series trucks 1970-1987, Wagoneer (SJ) models from 1972 to 1984, Cherokee (SJ) from 1974 to 1983, as well as in the full-sized Grand Wagoneer from 1984 to 1991 - becoming the last carbureted engine used in an American-built vehicle. The 360 V8 was also installed in the Bricklin SV-1 sports car for 1974 model year.
The 360 was the last AMC V8 to be manufactured. It continued to be produced after Chrysler bought American Motors in 1987 as the standard engine in the Jeep Grand Wagoneer through 1991, with the only modification being the "360" casting replaced with "5.9L" on the side of the block.
The AMC 390 6,384 cc (6.4 L) V8 engine produced 325 hp (242 kW; 330 PS) in all except the Rebel Machine. This muscle car engine was rated at 340 hp (254 kW; 345 PS) due to a different intake. Production only lasted one year (1970) before it was stroked to become the 401 cu in (6.6 L). Like the Gen-2, the maximum factory recommended overbore is only 0.020 in (0.508 mm), though they are commonly bored 0.030 in (0.762 mm).
The 401 has a displacement of 401.11 CID (6,572.9 cc) which produced 330 hp (246 kW; 335 PS) gross in 1971 and 255 hp (190 kW; 259 PS) net from 1972 to 1975. In 1976 it was rated at 215 hp (160 kW; 218 PS). Like the 390, the 401's crankshaft and connecting rods are forged steel. Like the 390, factory recommended overbore is only 0.020 in (0.508 mm), but commonly bored by 0.030 in (0.762 mm). It was last produced in 1979. Their combination of rarity, toughness, and excellent power output means that 401 engines are highly sought after.
The 401 was available in the Javelin, Matador, and Ambassador car lines and in Jeeps from its introduction in 1971 through 1974. In 1975 and 1976, emission controls, insurance rates, and high gasoline prices meant the 401 was available on the large Matador model, and then only for police department orders. Buyers of full-sized Jeeps (Wagoneer, Cherokee, J-10 and J-20) could order a 401 until 1979. This engine was also supplied to International Harvester for use as an optional engine in International's Light Line pickup trucks and Travelalls from late 1973 through 1974.
There was also a "Service Replacement" block made as a modified GEN-3 design. This is a 401 casting (same casting number) without the displacement cast into the side and with a 360 bore and thicker deck. In theory this single block could be built as any 343-401 GEN-2 or GEN-3 engine. A dealer could stock one or two blocks to use for warranty replacement.
The main bearing web area was thicker in the 390, 401 and SR blocks, thick enough that two additional bearing cap bolt holes could be drilled and tapped for an aftermarket four bolt main cap, providing a stronger bottom end. AMC never built a factory four bolt main block, they sold aftermarket four bolt main caps through their Group 19 performance parts program.
The SR block also sold as a heavy duty racing block, which is speculated to be the real reason it was produced in the first place. It appeared in 1970 in time for the 1971 Trans-Am racing season, and was used in the factory Trans-Am backed cars prepared by TRACO for Penske Racing, with Mark Donohue the primary driver. Since it was a standard factory part it did not have to be homologated under T/A rules, and was not used in the 2501 "Mark Donohue" Javelins built to homologate the "duck tail" spoiler. Those received standard 360 or 390 engines, buyers choice. The only thing special about the Donohue Javelins were the spoiler and "Mark Donohue" signature decals. That makes it an easy model to clone, and makes it difficult for automobile collectors to identify original vehicles.