40 Jp jpmagazine.com OCTOBER 2019
DON’T DITCH THAT AMC V-8
also appreciate the venerable AMC V-8
that fullsize Jeeps (and lots of CJs) were
outfitted with between 1965 to 1968
and again in 1970 and 1991? That got us
thinking. Maybe it’s time to explain why
you shouldn’t ditch that AMC V-8.
We’ve taken a look at Jeep’s power-
plant past and have compiled a bit of
h istor y — as well as some adv ice on how
to build a great AMC V-8. We’ve also
had the pleasure of interviewing Larry
Ofria, the man who helped AMC design
the dogleg heads in the late 1960s. He is
a n eng i ne g u r u whose raci ng h istor y goes
back more t ha n 50 yea r s. Perhaps t h is w i ll
help you make the right decision when the
next opportunity arises to build a custom
AMC V-8.
The Original AMC V-8:
1956 to 1967
CEO George Romney ordered the
original AMC V-8 to be built in 1954.
Less than two years later, the AMC
executive had his new V-8 ready to debut
to the world. With a forged crankshaft
and connecting rods, this overhead valve
pushrod engine became the muscle car
powerplant for Rambler, Nash, and
Hudson vehicles—and the workhorse
for the Jeep trucks and Wagoneer. The
engine came in three sizes—the 250ci,
the 287ci, and the 327ci—all with the
same stroke but different bores. The
287ci replaced the 250ci after a couple
years, and the 327ci was released a year
after the original 250ci but with hydraulic
lifters (that the 287ci also later got).
There is occasionally some confusion
as to what powered the first V-8 J-trucks
and Wagoneers, but it was not a Chevy
327 (which did not emerge until five years
after the AMC 327). From 1965 until
early 1968, Jeep offered the AMC 327
block as the Vigilante V-8.
Size Years Bore Stroke Special Notes
250ci 1956 to 1961 3.500 3.250 • The original AMC V-8 developed by Dave Pot ter
- Had solid lif ters
287ci 196 3 to 1965 3.750 3.250 • Replaced the 250ci engine - Had 0.25 inch more bore (total of 3.75 inches bore)
327ci 1957 to 1967 4.000 3.250 • Known as the “Vigilante V-8” in Wagoneers and
trucks (1965 to early 1968)
Size Years Bore Stroke Special Notes
290ci 1966 to 1969 3.750 3.280 • Used for Trans-Am racing
3 4 3ci 1967 to 1969 4.080 3.280
390ci 1968 and 1969 4.165 3.574 • High-nickel-content block- Forged cranks and connecting rods
- Heavier main bearing support webbing
The Second Generation:
1966 to 1969
By the mid-’60s, AMC’s first-
generat ion V- 8s were old hat, a nd t he
company eagerly introduced its second
generation of V-8s in 1965. The new V-8
shared the same basic design, but it was
a physically smaller block and utilized a
more modern thin-wall casting technol-
ogy that allowed it to drop around 60
pounds compared to the first-gen V-8.
The bore center remained the same, and
different displacements were made using
a combination of bores and strokes. These
engines had rectangular port heads that
f lowed well, and AMC’s new V-8s were
known for making great power with verylittle headwork. But AMC was not yet
where it wa nted to be i n raci ng — a nd not
yet satisfied.
In 1968, AMC released the AMX
390ci engine with a higher-nickel-content
block, forged crankshaft, and forged
connecting rods. It has been said that
the reason for the forged parts was that
AMC gave the engineers improper time to
properly test cast parts with the increased
power that the 390ci variant made, so they
went for overkill to be safe. It would be a
relatively low production number engine,
so the higher parts cost (of forged parts and
stronger block) was likely seen as a wash
since they could forego the testing.
You’ll notice there is a slight produc-
tion overlap in engine generations; the
Vigilante 327 V-8 made it into 1968 in
the Wagoneers, while the new second-
gen 290ci V-8 was released in 1966.
Interestingly, Jeep never used the second-
gen AMC V-8 and instead sourced a
Buick-derived 350ci with a very f lat torque
curve for 1968 until 1971. We have not yet
found a definite answer as to why.The AMC 401
If there is one AMC V-8 block to have, it’s the 401. Well, technically there are two
blocks to have. We have to include the one-year-only 1970 390ci that was made before
they increased the stroke by 0.11 inch. The AMC 401 is probably a better choice, but the
cool factor of the one-year-only variant is too much to pass up. Why a 401 block over
a 360 or 304? The 401 was a higher-nickel-content block that used a forged crankshaft
and connecting rods with larger 2.248-inch rod journal diameters. It has been stated
that the factory parts will survive 7,000 rpms in built-up engines. The thicker webbing
around the main bearings gives enough room to drill and tap two additional bolts to
accommodate aftermarket four-bolt main bearing caps if you desire to do so (AMC
V-8s were never four-bolt—and always two-bolt—mains from the factory). Hot rodders
loved them because they were not compression sensitive and they held together
under extreme force. AMC never had a big-block, but many Chevy, Dodge, Ford, and
Pontiac fans still complained about the large-displacement small-block AMC 401.There were only three years of AMC 390–
branded blocks: 1968, 1969, and 1970. The
’68 and ’69 were second-gen engines, while
the one-year-only 1970 390ci was a third-
gen with a special rod-and-piston combo to
achieve 11 ci less than the 401. The 390s were
never offered in Jeeps.