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Main >> Engine >> Factory >> AMC V8 Engines

AMC V8 Engines 

The Jeep AMC 304 V8 engine.
Photo courtesy Brian Coday.

AMC went through three generations of its V8 Block, though the most famous are its third generation blocks used in muscle cars. Generally, AMC V8s are considered "Small Block" due to exterior size and their maximum displacement. This usually refers to the later engines.

GEN-1 Nash/Hudson/Rambler V-8s (1956-1966)

Many members of the AMC hobby refer to this engine family as the "GEN-1" AMC V8. It was created almost by accident. 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.

An incensed 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 640 lb (290 kg) - forged crankshaft and rods, as well as most other parts. The stroke for all GEN-1 V8 is 3.25 inches. Engine displacement varied by bore alone since it was cheaper to cast different blocks than to forge multiple crankshafts (forged cranks and rods were used in all engines until the early sixties when casting technology caught up to required strength in such parts). The 250 in (4.1 L) has a 3.50-inch bore, 287 in (4.7 L) 3.75-inch, and the 327 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 1950's, the block features a deep skirt where the casting extends below the crankshaft centerline. The oiling scheme is shared with the Chevrolet Small-Block engine the Ford FE engine using a third oil passage above and between the lifter banks to feed oil to the lifers, cam and crankshaft.

AMC's first V-8, the 250, was used in American Motors Corporation automobiles from 1956 through 1961. As the name implies, it had 250 CID (4.1 L) of displacement and 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 57 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.

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

The AMC 327 was similar to the 287, but displaced 327 cubic inches (5.4 L) due to the bore increase to 4.0 inches. Unlike the 250, the 327 came with hydraulic valve lifters.

This engine debuted in a special edition Rambler Rebel of which only 1500 were made. All had silver paint with a gold-anodized "spear" on each side. This was to be the first electronic fuel injected (EFI) production engine, but teething problems with the Bendix "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), and the production 4V carbureted model at 255 hp (190 kW). All the EFI cars were reportedly converted to 4V 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. From this one could derive that the 1957 Rebel (and EFI in general) was ten years ahead of its time.

The 327 was not available in any other Rambler models in 1957 other than the Special Edition Rebel. The Nash Ambassador and Hudson Hornet "Special" models were dropped after 1956, replaced by standard 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. 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 was also sold to Kaiser Motors from 1965 to 1967 for use in the early Wagoneers and the Gladiator pick-ups. Jeep called it the "Vigilante" V8. Kaiser-Jeep switched to Buick 350s in 1967 to power these vehicles. The GM engine was used up to 1970 when Jeeps once again were powered by AMC. That was the year American Motors acquired the Jeep Division of Kaiser.

There was a low and high compression version of the 327 starting in 1960. Prior to 1960 all were high compression. All low compression models used a 2V carburetor and all high compression models received a 4V carb. "Low" compression was 8.7:1, high 9.7:1. Piston top design changed compression, the heads were identical.

GEN-2 AMC Short-Deck V-8 (19661970)
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, 343, and 390) 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. 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. Bore center measurement was kept the same as the GEN-1 AMC 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 V-8s 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.

The GEN-2 AMC V-8 was first introduced at 290 CID (4.8 L) in 1966. It was used exclusively in the American model the first year (some reports indicate a few late production Classics had 290s substituted for 287s, but that has not been substantiated). The 343 CID (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.

The GEN-2 AMC V-8 was first introduced at 290 in (4.8 L) in 1966.

The base 290 in (4.8 L) 290 produced 200 to 225 hp (149 to 168 kW) with a 2V and 4V carburetor, respectively. It was built from 1966 through 1969. It has a 3.75 in. bore (95.25 mm) and 3.28 in. (83.31 mm) stroke.

The base 290 CID (4.8 L) 290 produced 200 to 225 hp (149 to 168 kW) with a 2V and 4V 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. CASTING LAST 3 #


The 343 in (5.6 L) came out in 1967.

The 343 in (5.6 L/5622 cc) 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 4V carburetor version was 280 hp (209 kW) and 365 ftlbff (495 Nm) gross. This version had a 10.2:1 compression ratio.

AMX 390
The AMX 390 in (6.4 L) arrived in 1968.

In addition to the largest bore and stroke, the 390 CID (6.4 L) 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 (235 kW) 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.

The big AMC engines were known for durability in cranks and rods when used for performance.

The GEN-2 AMX 390 produced 315 hp (235 kW) 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", though they are commonly bored 0.030".

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 and 360, 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.

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. 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.

The AMC 360 had a displacement of 359.80 CID (5,896.1 cc). 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 built for car or truck use in North America.

The AMC 390 in (6.4 L) 390 produced 315 hp (242 kW) in all except the Rebel Machine, which produced 340 hp (254 kW) due to a different intake.  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. Like its GEN-2 cousin, the maximum factory recommended overbore is only 0.020 in, though they are commonly bored 0.030 in.

The 401 had a displacement of 401.11 CID (6,572.9 cc) 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. Today, due to 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, government manipulation on the automotive side of the business forced AMC to reduce the 401's availability to just the Matador, 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.

"Service Replacement" Multi-Displacement Block
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. It was 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. 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 homolgate the "duck tail" spoiler. Those received standard 360 or 401 engines.

Also See:

AMC V8 hp/Torque, Compression & Bore/Stroke by year

Ford Engines - 4 Cylinder, 6 Cylinder, 8 Cylinder, 10 Cylinder, 12 Cylinder Ford Engines

Ford V8 Engines - 8 Cylinder Engines manufactured by Ford

Ford 351 Cleveland V8 Engines - 351 cubic inch V8 Engines manufactured by Ford

AMC V8 Engines - From GEN-1 Nash/Hudson/Rambler V-8s (1956-1966) through to the GEN-3 AMC Tall-deck (1970-1991)

AMC V8 hp/Torque, Compression & Bore/Stroke by year






The Jeep AMC 304 V8 engine.
Photo courtesy Brian Coday.




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