AMC V8 engine

American Motors Corporation (AMC) 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.

GEN-1 Nash/Hudson/Rambler V8s (1956-1966)
This engine family is now referred to as the "GEN-1" AMC V8, but in its time it was known as the Rambler V8. As part of a larger plan of merging Packard, Nash, Hudson, and Studebaker, AMC President George W. Mason had a verbal agreement with Packard that the two companies would supply parts for each other when practical. AMC started buying Packard V8s in 1954 for the big 1955 Nash Ambassador and Hudson Hornet. These were supplied with Packard "Ultramatic" automatic transmissions - exclusively. Packard sent AMC some parts bids, but were rejected as too expensive. George W. Romney, AMC's new head decided against further relationships with Packard.

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 come in and help develop the engine. Potter had previously worked on a V8 design for Kaiser, and had the experience necessary to take the engine from drawing board to full production in just under 18 months, an extraordinary engineering feat at the time—slide rules were the norm because there were no computers.

All these engines share common external dimensions, weight - about 601 lb (273 kg) - forged crankshaft and rods, as well as most other parts. The stroke for all GEN-1 V8 is 3.25 inches. Engine displacement The 250 cu in (4.1 L) has a 3.50-inch bore, 287 cu in (4.7 L) 3.75-inch, and the 327 cu in (5.4 L) a 4.0-inch bore. Bore size is cast on the top of the block near the back of the right bank cylinder head. This is difficult to see with the engine installed in a Rambler due to the close proximity of the heater. It can be done with a small inspection mirror. 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 oiling scheme is similar to the Chevrolet Small-Block engine for feeding oil to the cam and crankshaft first, then to the lifter galleries.

250
AMC's first V8, the 250, was used in American Motors Corporation automobiles from 1956 through 1961. It was a modern (for the time) 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 used 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 "Rebel" and designated as a different series. However, 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.

287
In mid-model year 1963, AMC introduced a 287 cu in 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 used hydraulic valve lifters. Only 2-barrel models were produced, there were no 4-barrel options from the factory for the 287 as this was the economy model V8. The 287 was produced through 1966.

327
The AMC 327 was similar to the 287, but displaced 327 cu in due to the bore increase to 4.0 inches. Unlike the 250, the 327 came with hydraulic valve lifters.

The AMC 327 engine debuted in a special edition Rambler Rebel of which only 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 legacy Nash Ambassador and Hudson Hornet "Special" models were dropped after 1956, replaced by standard "Rambler" wheelbase models with the 327 V8 instead of the 250 V8. When the big Nash and Hudson cars were dropped after 1957, they were replaced by the 1958 "Ambassador by Rambler"—a stretched Rebel (Rambler V8) with the 327 V8 instead of the 250 engine. The 327 was exclusive to the Ambassador line and could not be ordered in a Rebel or Classic through 1964. For 1965 and 1966 the 287 and 327 were both available in the Classic or Ambassador.

The 327, in two barrel form only, was sold to Kaiser Motors from 1965 to 1967 for use in the early jeep Wagoneers and the Gladiator pick-ups. Jeep named it "Vigilante" V8. Kaiser-Jeep switched to Buick 350s in 1967 when AMC discontinued the engine. The Buick V8 engine option was used up to 1970 when Jeeps once again were powered by AMC, the year American Motors purchased Jeep Corporation from Kaiser.

There was a low- and high-compression version of the 327 starting in 1960. Prior to 1960 all 327s were high compression. All low compression models used a 2-barrel carburetor and all high-compression models received a 4-barrel carb. "Low" compression was 8.7:1, high 9.7:1, effected by cast combustion chamber volume.

Electronic fuel injection
The AMC 327 was to be the first commercial electronic fuel injected (EFI) Electrojector production engine.[1] 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 would only be available after June 15.[2] 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.[3]

The EFI 327 was rated at 288 hp (215 kW) and the regular 4-barrel carbureted model at 255 hp (190 kW).[4] 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.[2] All the EFI cars were reportedly converted to 4-barrel carb before being sold; none are known to have existed outside the engineering department at AMC. The main problem was that vacuum tube and early transistor electronics just could not keep up with the demands of "on the fly" engine controls. Ironically, Bendix licensed patents based on the 1957 the design (patent dated 1960) to Bosch, who perfected it as the basis for their D-Jetronic injections system, first used in 1967.

GEN-2 AMC Short-Deck V8 (1966–1970)
The new-generation AMC V8 was first introduced in 1966. It is sometimes referred to as the "GEN-2" AMC V-8. 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 V-8 (4.75 in.) 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 V-8 was first introduced at 290 cu in (4.8 L) in 1966. It was used exclusively in the American model the first year. The 343 cu in (5.6 L) came out in 1967 and the AMX 390 CID (6.4 L) arrived in 1968. These engine blocks were unchanged through the 1969 model year.

The head used during this time are the so-called rectangle port, named after their 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 AMX 390 used the same larger valve heads, 2.025 in (51.4 mm) intake and 1.625 in (41.3 mm) exhaust.

290
The base 290 cu in (4.8 L) 290 produced 200 to 225 hp (149 to 168 kW) with a 2-barrel and 4-barrel carburetor, respectively. It was built from the mid-1966 model year through the 1969 model year. It has a 3.75-inch bore (95.25 mm) and 3.28-inch (83.31 mm) stroke. Only 623 cars were built in 1966 with the 290. These should all be "American" models, but it has been rumored that a few "Classic" models may have received 290s as inventory of 287s ran low. This is unlikely, as some 287 engines would have been kept in inventory for warranty replacements.

343
The 343 cu in (5.6 L) 343 has a 4.08 in (103.6 mm) bore and 3.28 in (83.31 mm) stroke. The basic 343/2V produced 235 hp (175 kW) and was built from 1967 through 1969. Output for the optional 4-barrel carburetor version was 280 hp (209 kW) and 365 ft·lbf (495 N·m) gross. This version had a 10.2:1 compression ratio.

AMX 390
In addition to the largest bore and stroke, the 390 cu in AMX 390 motor also got heavier main bearing support webbing and a forged steel crankshaft and connecting rods. Forged cranks and rods were used for known strength—there was inadequate time for testing cast parts for durability without slipping AMCs desired introduction schedule. Once forging dies were made it wasn't cost effective to test cast parts due to the relatively low number of engines produced. This was continued with the 401. The bonus was that the big AMC engines, when used in performance applications, never had problems with rods breaking, unlike other US companies' large displacement small block engines. The GEN-2 AMX 390 produced 315 hp and was built in 1968 and 1969. Bore is 4.165 in (105.791 mm) and stroke is 3.68 in (93.47 mm). Maximum factory recommended overbore is only 0.020 in, though they are commonly bored 0.030 in. In 1970, AMC changed the head design to the later known "dog-leg" exhaust port.

GEN-3 AMC Tall-deck (1970-1991)
In 1970, all three blocks grew in deck height and gained a new head design. These changes made this the third generation of AMC V-8, hence it is sometimes referred to as the GEN-3 AMC V-8. The stroke and deck height on the 290 and 343 was increased by 0.16 in (~5/32 in), becoming the 304 cu in and 360 cu in, 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 stroked by 0.16 in to become the 401.

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 (by a machine shop) and slotting the center holes.

There is a persistent myth about 1970-mid 1971 "319" or "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.

304
The 304 had a displacement of 303.92 CID (4,980.3 cc) which produced 210 hp (157 kW) in 1970-71 and was built starting in 1970.[5] Later models produced less power from the factory, going down yearly. 1972-78 models were rated at 150 hp (112 kW). It was rated at 130 hp (97 kW) in 1979, the last year it was installed in passenger cars, and 125 hp (93 kW) in 1980-81, the last years it was used in Jeep vehicles.

360
The AMC 360 had a displacement of 359.80 CID (5,896.1 cc).[5] The 2-barrel produced 235 hp (175 kW) to 245 hp (183 kW) in 1970 to early 71 while the 4-barrel produced 285 hp (213 kW) to 295 hp (220 kW), 175 hp (130 kW) to 220 hp (164 kW) from mid-1971 to 1975, 140 hp (104 kW) to 180 hp (134 kW) in 1976, 129 hp (96 kW) in 1977, and 160 hp (119 kW) from 1978 to 1991.

It was the last AMC V8 to be manufactured. It was used exclusively in Jeep J-series Trucks 1970-1987, Jeep Wagoneer models from 1972–84, Cherokee from 1974 to 1983, and Grand Wagoneer from 1984 to 1991 - becoming the last carbureted engine used in an American-built vehicle. It was also installed in the Bricklin SV-1 car in 1974 only.

390
The AMC 390 cu in (6.4 L) 390 produced 325 hp (242 kW) in all except the Rebel Machine. This muscle car engine was rated at 340 hp (254 kW) 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 its GEN-2 cousin, the maximum factory recommended overbore is only 0.020 in, though they are commonly bored 0.030 in.

401
The 401 had a displacement of 401.11 CID (6,572.9 cc)[5] which produced 330 hp (246 kW) gross in 1971 and 255 hp (190 kW) net from 1972 to 1975. In 1976 it was rated at 215 hp (160 kW). Like the 390, the 401's crankshaft and connecting rods are forged steel. Like the 390, factory recommended overbore is only 0.020 in, commonly bored to 0.030 in. It was last produced in 1979. Their combination of rarity, toughness, and excellent power output, 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 full size pickup trucks and Travelalls from late 1973 through 1974.

"Service replacement" blocks
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 tough on AMC hobbyists.