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AMC V8 Engines
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 in³ (4.1 L) has a 3.50-inch bore, 287 in³ (4.7 L) 3.75-inch,
and the 327 in³ (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
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 (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, 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 in³ (4.8 L) in 1966.
The base 290 in³ (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
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 #
BOLCK=062DE CRANK=451-C HEAD =453
The 343 in³ (5.6 L) came out in 1967.
The 343 in³ (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 ft·lbff (495 N·m)
gross. This version had a 10.2:1 compression ratio.
The AMX 390 in³ (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
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 in³ (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.
hp/Torque, Compression & Bore/Stroke by year
- 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
AMC V8 Engines - From GEN-1 Nash/Hudson/Rambler
V-8s (1956-1966) through to the GEN-3 AMC Tall-deck (1970-1991)
hp/Torque, Compression & Bore/Stroke by year
Jeep AMC 304 V8 engine.
Photo courtesy Brian Coday.