42 Jp jpmagazine.com OCTOBER 2019
DON’T DITCH THAT AMC V-8
The Third Generation
(aka Second-Gen Mark II):
1970 to 1991
Eager to do even bet ter i n Tra ns-A m
racing, the second-generation V-8 was
short lived. In 1970, AMC released a very
similar but improved version with a taller
deck heig ht a nd i mproved dog leg heads.
This was the final and best version of the
AMC V-8. While the second-gen version
was good, the taller deck height allowed
for a larger displacement and the dogleg
heads flowed even better than the already
i mpressive rec ta ng u la r por t heads. A nd
perhaps that is the answer as to why the
second-gen engine never made it into
Jeeps; maybe AMC knew it would soon
be making a “Mark II” version of the
engine and decided to wait with the Jeeps,
sourcing Buick engines in the interim.
How good was that dogleg head? It’s
said it was so good that, in stock form,
it could outf low even the best custom-
ported and -polished Chevy, Ford, or
Dodge heads of its day. This was the
engine AMC had been waiting for to give
it the edge in Trans-Am racing. The 290ci
turned into the 304ci, the 343ci became
the 360ci, and the AMX 390 became
the mighty 401—the ultimate factory
powerplant to ever outfit a Jeep. It should
be noted that there was a one-year-only
1970 390ci third-generation engine prior
to the 401. AMC accomplished this with
a special rod-and-piston combination for
a smaller stroke to keep the displacement
at 390 ci. It is said the reason this was done
was due to the popularity of the AMX 390
name, and to kill that success after only a
two-year run would be silly. A year later,
the 401 was born.
Considering when these engines
were designed, have you ever thought
to yourself, Why the 304ci? It was a time
just pr ior to a ny f uel c r u nch or em issions
restrictions—when bigger was always
better. The 304ci still sported the same
stroke as a 360ci but with a smaller bore
and was barely (laughably) better on
fuel. So why bother making the smaller-
displacement 304? A good reason
could be found within the rule books of
Trans-Am racing. The engine size limit
of a Trans-Am car: 305 ci.
Unfortunately, all good things come
to an end. Starting in 1980, the 401 was
dropped after being practically suffocated
by ill-working emissions equipment in
its final years. The 304 was dropped by
the end of 1981—likely due to the fact
that AMC’s six-cylinder was making
more horsepower, and its emissions
were no bet ter t ha n t he 360’s. T he 360
stuck around until 1991, powering theThis is the dogleg head that replaced the
rectangular ported heads and gave AMC the
winning edge they needed.Size Years Bore Stroke Special Notes
30 4ci 1970 to 1981 3.750 3.4 4 0 • Used in various Jeep products as well as Trans-
Am Racing (AMC’s last championship would be in
1976 with a Javelin)
- Same stroke as 360ci with smaller bore
360ci 1970 to 1991 4.080 3.4 4 0 • Longest production run of any AMC engine - Most common size of AMC blocks
390ci 1970 4.165 3.574 • One year only: special rod and piston for smaller
stroke to stay at 390ci - High-nickel-content block
- Forged crankshaf t and rods
4 01ci 1971 to 1979 4.165 3.680 • Widely considered the ultimate AMC block - High-nickel-content block
- Forged crankshaf t and pistons
- Heavier main bearing support webbing
- Used in 1971 to 1978 Jeep J-trucks, Wagoneers,
and Cherokees
SR block Beginning 1970 4.080 N/A • Service Replacement block with same high
nickel casting as 4 01 but bore of 360
- Also sold as a heavy-dut y racing block
- Did not have displacement size cast into the side
Fuel Injection Options
The AMC V-8 was never fuel injected from the factory in a Jeep product. In fact,
it was one of the last carbureted engines built in North America—up until 1991.
But there are some electronic fuel injection options out there. One of our favorites:
Howell’s plug-and-play throttle-body kit. It’s 50-state legal, gets rid of a lot of terrible
emissions equipment and vacuum hoses, and runs beautifully, giving smooth power
response and increasing fuel economy. There are two- or four-barrel systems, but
Howell tunes them specifically for your engine alterations and sends you a ready-
to-go EFI system that bolts on top of any standard intake manifold for a pretty
reasonable price.wood-paneled Grand Wagoneers that so
ma ny of us have fond memor ies of r id i ng
in. It should be noted that the Wagoneer
had the longest production run of any
Jeep, consequently giving the AMC 360
V-8 an extremely long life as well.The Inventor of the
Dogleg Heads
To get better insight into the last and
best of the AMC V-8 blocks, we took a
trip over to Northridge, California, to
meet with Larry Ofria at Valley Head
Service. The name of the shop—rather
humble—does not begin to tell the
stories of what has come from inside.
The Thunderpower 32-valve heads are a
Valley Head product, and Ofria’s original
Dry Sump Pump external oiling system