Super
Stock and Drag Illustrated magazine, August 1972
Parts
And Pieces From AMC in order to build any of the V8 AMC engines, from the 290
to the 401, for performance use, you’ve got to know about family’s and
interchangeability. Here it is, folks.
THERE
ARE A LOT OF performance enthusiasts running around today with heads full of
wrong ideas about American Motors cars and engines. The general opinion is that
they are not suitable for performance or racing use, and that opinion is about
as far from the truth as an opinion can be. The popularity of these machines is
only now starting a period of deserved growth, but the pieces have been there
all along, never receiving any real attention from large numbers of builders,
though quite capable of impressive performances and incredible longevity. The
fact is, inch for inch and pound for pound, the American Motors
V8
engines are among the best available for durability and performance.
Like
any engine, the AMC V8 can be made to perform with an investment of money,
time, and planning, using many stock parts and a few items from the
unfortunately limited supply in the performance aftermarket. With the help of
AMC’s Performance Activities Department, we have compiled the information
necessary to build up AMC V8 engines for street and drag strip use, and we’ll
try to present it in a clear and orderly fashion, with as many alternatives for
the builder as possible, a few no-no's, and some definite recommendations for
the engine-building process.
All
recent AMC engines are very light, using aluminum covers, thinwall castings, lightweight
power accessories, while developing good power and superior flow.
BLOCKS
Selection
of a block will depend on what the AMC builder has to start with, the ultimate
purpose for the car (class, brackets, street, Modified, SS, or Stock), and the
money available for completion of the project. We’ll restrict all of our engine
discussions to ’68 and later engines, from 290 cubic inches on up. In order of
size, there are the 290, 304, 343, 360, 390, and 401 V8 engines in the ’68 to
'72 lineup. Taking the engines as groups or families, the 290 and 343 form a
group, with 3.75" bore and 3.28" stroke for the 290, and a 4.08"
bore and 3.28" stroke for the 343. Obviously, the 343 is a 290 with an
increase of .33" in the bore. The next family is formed by the enlarged
versions of the previous two engines, the 304 and 360 blocks. The 3.75"
and 4.08" bore remained the same, and stroke was increased by .160"
to 3.44" in both engines. The 390 engine is by itself at 4.165" and
3.574" bore and stroke, and the 401 measures 4.165" by 3.68".
The engines are further separated in other respects, in that engines up to 1969
were made with one block deck height, and 1970-72 engines used another deck
height. This presents problems when heads and manifolds are installed, and
we'll get into that later. Another basic block item to note is that
290-304-343-360 blocks are made for use with cranks having rod journal sizes of
2.09" while 390 and 401 blocks use 2.248" rod journals. Main bearing
journals and bore centers on all AMC V8 engines are exactly the same at
2.747" and 4.75", respectively. For maximum performance, we would
recommend using the 401, even though it will cost, since it’s the largest and will
fit the same way as the baby 290.
For
drag racing use, any of the V8 engine blocks can be expected to deliver
performance and longevity. They’re all thinwall castings, light and strong, and
they’ll accept heavy modifications short of supercharging and fuel with no
problems. For the cautious, though, the 390-401 blocks are indicated, since
they have more than twice as much beef in the main bearing area, and can all be
machined to accept four-bolt main bearings caps from an outside supplier such
as Milodon or Summers Brothers (1970 and later blocks only).
Maximum
overbore recommendation for 290-304 engines is 3.830", the 343-360 is
4.160", and the 390-401 series can be punched to a maximum of
4.1875". Cylinder bore finish should be set to 30-40 micro inches, which
is a step rougher than the factory 20-30 micro inch finish, and the cross-hatch
angle in the bores should be between 45 and 60 degrees. Of course, any block
being modified for racing or increased performance should be cleaned thoroughly
with detergent and water about four times, blown dry with an air hose, and
carefully inspected for cracks. All remaining casting flash should be buzzed
off with a highspeed hand grinder, with special attention to the lifter galley
area. All sharp corners should be broken with a heavy-duty file to reduce heat
and stress buildup, and the extremely generous lifter bores should be honed out
for free travel. It’s also a good idea to open up the main oil passages in the
block to increase flow through the engine.
BOTTOM
END
In
discussing bottom end pieces, once again, "families" must be
explained. As noted earlier, all AMC V8 cranks have 2.747" main journals,
while engines to and including the 360 use small rod journals of 2.09"
diameter and the 390 and 401 use 2.248" rod journals. The 290-360 cranks
are nodular iron cast units, while 390 and 401 cranks are forged steel and stronger
by far than the cast ones. However,
drag racing engines of 290-360 cubic inches can use the stock cranks if they
are properly magnaflux checked, cross-drilled for oiling, and treated to a
Tufftride and polish job by competent crankshaft specialists. In either case,
cast or forged, crankshafts should be chosen carefully, checked for
straightness and index, and handled by machinists who know what they are doing.
When it
comes to building an AMC engine of specific displacement, the whole problem of
mating blocks to cranks, rods, pistons, and pins will have to be dealt with,
and there are important differences in size and quality in all of these components.
The small 290-360 rods use 2.09" big ends, with .931" pin bores and
pin lengths of 3.187". These 290-360 rods are all 5.875" long, and
they were all made of cast iron, which means that they can only accept so much
stress, even after magnaflux inspection, shot-peening, and polishing. Early
(’68-’69) 390 rods had a big end diameter of 2.248" but were only
5.790" long. Late 390 and all 401 connecting rods use 2.248" crank
diameters, 1.00" pin bores, 2.94" pin lengths, and center-to-center
lengths of 5.858", and all 390-401 con rods are forged steel and
recommended for performance work after sizing, Magnafluxing, shot-peening, and
polishing. Factory recommended clearances for racing engines are
.0065-.009" piston-to-wall, for forged pistons.012-.017" ring end
gap, .012-.016" rod side clearance, 0025-.003" main bearing
clearance, .002-.0025" rod bearing clearance, and .080-.100"
piston-to-valve clearance in all cases.
-------------------------------
TOP -
Modern high-flowing heads use what’s called a dog-leg exhaust port, and no
other AMC head will flow half as well, race-bred or not. The dog-leg heads will
go right on to 70-up engines, but need a special dowel setup for use on earlier
engines.
SECOND
- Intake ports on late AMC heads are large and fast, and a good professional
porting job will yield great increases in flow and performance when done with a
proper valve job and milling.
ABOVE -
Late model (’70-up) big blocks have twice as much main bearing web beef, will
accept 4-bolt mains like these.
LEFT -
Late heads have 2.02" intake and 1.625" exhaust valves.
-------------------------------
RIGHT-
Cutaway shows typical construction of an AMC Dana rear, which uses a ring gear
of 8.9" diameter, hefty pinion, and small ring width. Axles can be used for
mild racing if they are machined for new longer and wider keys, but aftermarket
billet axles are best for serious racing use. Ration selection is very good.
BELOW
RIGHT - Late model 401 crankshaft is forged, as are late 390 units, and both
are okay for racing if they’re properly treated before installing. Cast cranks
for small engines will also take a lot of abuse.
RIGHT -
Connecting rods for the AMC engines belong to three basic families, with
5.875" rods for 290-300 engines, 5.790" rods for '68 and ’89 390
engines, and 5.850" rods of forged steel for late 390 and 401 engines. As family
changes, the size of the big end bore and the pin bore also changes.
-------------------------------
Pistons
for American Motors V8 engines are a problem. The factory does not engage, like
some others, in producing or having produced oversized, extra-compression
pistons for owner or dealer installation, so that, other than the aftermarket,
where JE Engineering and Venolia offer special forged racing pistons for pretty
good prices, the plan is to use the highest compression piston offered for any
of the six engines under discussion, with the appropriate matching
small-cc-displacement heads and big valves. Following this plan, the 290
engine' would use the ’69 10:1 4-barrel piston. The 304 would take the ’70
model year 9:1 unit. The 343 engine could best use the 1969 10.2:1 4-barrel
piston that was used with 51 cc heads. The highest compression piston ever used
in the 360 engine was the ’70 290 hp 4-barrel model, and the old standby 390
should use the 1970 325 hp 10.2:1 pistons (because of severely limited
supplies, we will not include in this story any mention of Rambler SC/Rambler,
Rebel Machine, Hurst SS/C ’69 AMX, or Trans-Am Javelin engine parts for the
various engines. Even if a source of supply could be found, prices for some of
these pieces are astronomical). The new 401 engine will benefit most by
installation of ’71 330 hp, 9.5:1 pistons. Pistons for all engines should be
properly machined and fitted with recommended clearances. The factory
recommends conversion of rods to full-floating configuration in heavy duty
applications, with .0008-.0012" pin to con rod clearance, and
.0007-.0010" pin to piston clearance. Oiling holes should be drilled on
the small ends, and the piston pin bores must be grooved to accept pin locks
such as Tru-Arc rings.
CYLINDER
HEADS
Once
the builder has opted for a block and bottom end assembly, head selection is
the next big decision, and it’s a complicated one. The various combinations of
chamber cc volume, port configuration, and valve sizes in AMC V8 engines
between 1968 and 1972 can cause a great deal of confusion.
Basically,
the 290 and 304 engines used small valves, with 1.787" intake and
1.406" exhaust head diameters. The 343 engines, the ’70 model 360, and the
'68-’69 390 had intermediate valving, with 2.02" intakes and 1.625"
exhausts, but ’70 and later 360, 390, and 401 blocks used the big 2.02"
in-takes with larger 1.68" exhaust valves. So far, so good. The problem is
that the only heads that really flow well are the later "dog-leg"
exhaust port models with convex port floors, as opposed to the earlier ’68-’69
rectangular exhaust port heads with concave floors. The 'dog-leg' heads flow a
full 50% more fuel/air charge than the older heads, and these are the ones used
by the AMC Pro Stock fleet.
The hot
set-up then, in cylinder heads, is a dog-leg exhaust port head, with the small
51 cc chamber used in pre-smog years, and with the larger intake and exhaust
valves, right?
The
problem is that there is no one cylinder head with all three features. Now, the
Performance Activities department tells us that the rectangular exhaust port
heads are not the hot tip under any circumstances, since they won’t flow as
well as a dog-leg setup even when they’ve been ported and polished. Three
choices remain. The 1970 360-390 head (3916291) having the 51 cc chambers,
dog-leg porting, and intermediate valves (2.02" and 1.625") is a good
bet, but you will have to resort to junkyards or hoarders, since they are not a
service replacement item any longer. If you can locate them, bore out the
exhaust valve seat to accept the 1.68" exhaust valve, and you’ve got all
three features in one set of heads. Of the parts available through AMC service,
the 1970 304 head (4487242) has 51 cc chambers, dog-leg ports, and small
valves, which can be replaced by big valves fairly easily. The added attraction
of the 304 head is that it’s available as a new replacement part at the
dealerships at a reasonable price. If you are willing to go the aftermarket
route for high compression pistons, the next best choice is the low-compression
58 cc ’71-’72 360-401 head. It has dog-leg ports, the biggest valves available,
and easy access through normal parts channels. Its part number is 8120126.
Performance
Activities has developed a complete plan for head modifications that work and
produce gobs of power. It’s not simple, and it must be followed to the letter
to get maximum gains. It starts with a spotfacing operation on intake seats
with a 2.40" cutter that has a 45º by.12" chamber, to get a
2.16" diameter at the outside edge (these and all other modifications are
for use with production large valves, 2.02" intake and 1.68"
exhaust).
When
the spotfacing is finished, the intake ports get a new throat bored into them,
1.815" in diameter and half an inch deep as measured from the spotface.
The exhaust seat then gets a similar spoffacing using a 2.06" cutter with
a 45º x.12" chamfer to get a diameter of 1.82" at the end of the
chamfer. Both spotfaces should then be blended into the rest of the chamber
with round file and emery cloth.
The
intake port then gets more attention, using a 45º cut out to 1.99" outside
diameter, followed by a 60º grind to 1.94" seat ID. Then a 40º cutter is
used to the extent that the 40º and 60º portions are the same width. The valve
guide boss is then blended to .040" from the guide hole. Engineers caution
that no metal should be removed from the inlet end of the port up to the point
where the turn starts toward the throat, with the exception of casting flaws.
Grinding at the turn should be done only as required to blend to the throat to
.10" minimum throat length. All remaining sharp edges should then be
blended.
Exhaust
ports in the heads get their own treatment, starting with a 45º seat ground to
1.64" outside diameter. A 60º cutter is then used to intersect the seat at
a diameter of 1.570". A throat radius of .730" is then ground to the
center of the valve guide but only for 180º of the circle, and placed in the
direction of exhaust gas flow. The throat is then blended to the port and then
end of the valve guide is likewise blended.
The
basic shape and size of both intake and exhaust ports should not be changed except
as necessary to match manifolds. The exhaust manifold port widths for these
engines are made wider than the ports in the heads to allow for thermal
expansion. When the big heads are used on 290-304 engines, the bores in the
block must be top-chamfered to clear valves, and in all cases the valve seat
spotfaces should be checked for interference with headgaskets.
The
valves themselves should be modified to take full advantage of the new,
smoother ports. Intake valves should be ground with a 45' face starting
at.045" outside the land length. The inside edge of the face should then
be ground at 20º to a 1.930" inside face diameter (face width should be
.075"). Exhaust valves have their inside face edges ground at 18º to
a,1.55" inside face diameter (face width is.085").
Keep in
mind that the aim of the information in this story is increased street
performance from basically stock engines ang parts. Any serious attempt at
building an AMC car for NHRA class competition in Stock or Super Stock requires
consultation with NHRA technical staff people and with AMC’s Performance
Activities
Department before starting out. We offer the information in this story as a
guideline for street and bracket machinery, for which there are virtually no
rules.
CAMSHAFTS
AND VALVE TRAIN
Visually
all modern-times AMC engines, Sixes and V8’s alike, have used hydraulic
camshafts, and all V8 engine cams use the same bearing journal diameters, so
that they all will interchange from engine to engine. The trouble is that all
of the standard V8 grinds are gentle as pussycats and are combined with soft
springs and spongy lifters. The single option available is the dealer-installed
kit, 4488413, for ’70-’72 engines only (tlute early kit, 4486719, for low-block
V8 engines, is no longer available through the dealer network). The 4488413 kit
contains everything in the valve train, and the grind is a 302º-302º, 98º
overlap, .477" lift profile. It’s plenty sufficient (with headers) to pep
up a stock engine, but there are so many aftermarket grinds available (see
separate listings of aftermarket parts) at better prices that the factory cam
kit pales in comparison. As far as swapping stock cams from one engine into
another, simply because they fit, there’s very little to be gained.
When
using aftermarket cams and valve train pieces, follow installation instructions
from the manufacturer, setting springs for heights and pressures to specs, and
d8-greeing the cam at whatever position is recommended. Without changing valve
sizes or weights from stock, it will be possible to pick up about
2500
rpm on top with almost any grinder’s cam and kit pieces, and the inclusion of
aluminum roller-tip rockers will boost rpm even more, though they are pretty
expensive items for street use.
INDUCTION
SYSTEMS
In this
area, there are again the 'families' to deal with. All 1966-69 intake
mani-folds will interchange with each other, since block and head castings and
bolt patterns were all the same regardless of displacement, so that 'instant
four-barrel' modifications can be made easy. Likewise, the ’70-’72 manifolds
are all the same, but because the two center mounting bolt locations have been
moved upward and inward, the late manifolds won’t fit on early blocks and vice
versa. Either way, all production 2- and 4-barrel manifolds are cast iron and
fairly efficient.
AMC
dealers do have a small selection of manifolds to sell, though, and the most
popular one is the 3199763 for ’70-'72 engines. It’s a dual plane cast iron
manifold that’s good to 6500 rpm, with boost over carburetor bolt patterns. For
earlier engines, the Edelbrock R4B is recommended by the factory. The most
radical factory manifold available is the aluminum dual-quad cross-ram for twin
Holleys, under number 4486228 for early engines, and 4488411 for ’70-’72 engines.
It’s not the easiest system in the world to cope with at low street speeds, but
it’s great on the top end, from 7000 to 7500 rpm. This manifold was
commissioned by AMC through Edelbrock and also carries Edelbrock part numbers
STR-11 for early engines and STR-11-70 for ’70 and newer engines. The cross-ram
should be used with twin 600 or 700 cfm Holley double pumper carburetors. The
recommendation for either the factory or Edelbrock R4B single-quad manifolds is
either the 780 cfm vacuum secondary carb or the 800 cfm double-pumper. Stock
carburetion on early V8 engines from AMC consisted of Carter WCD 2-barrels and
AFB 4-barrels with 1.44" primary and 1.69" secondary barrels. In
1970, the corporation switched over to the Ford Autolite 4300 model 4-barrel with
1.56" primaries and 1.69" secondaries, and while this carburetor is
not as widely favored as some others, it can be made to work with the normal
rejetting, float-setting, and pump-arm modifications.
As a
fillip item for use with trick mani-folds, American Motors does stock a
heat-blocked manifold gasket that also acts as a hot oil baffle over the lifter
galley. The three-piece set includes front and rear seals and goes under number
4488475 for engines to 1969, and 4488476 for ’70 and later engines. It’s a
small item but worth including on any hot street engine.
IGNITION
Standard
factory ignition systems for most recent V8 engines include single-point
distributors with vacuum advance, 12-volt negative ground supply systems, and
alternators. Spark plug cables are carbon-core, and Champion N12Y spark plugs
are installed at the factory. For high rpm consistency, the factory parts
system once included a Delco capacitive discharge ignition, 4485742, including
distributor, heat sink, coil, and wire harness, but it has officially been
discontinued and removed from the system, though there may be a few floating
around. The optional ignition system that remains is a Mallory dual-point unit
with coil, ballast resistor, and switch, carrying part number 4487900 for an
ordinary unit, and 4487901 for the distributor with mechanical tach drive. The
factory recommendation is 38-42º total advance, all in at about 2800 rpm. Naturally, the carbon core wire should be
discarded in favor of one of the aftermarket brands with heat resistant coating
and solid copper or steel cores. Low budget AMC builders could retain the stock
distributor, disconnect the vacuum advance system, install heavily sprung
points, and replace the wiring and coil, but it’s far simpler to install a
complete, integrated system such as the AMC/ Mallory or other high performance
ignition.
DRIVELINE
The 10
1/2" Borg & Beck clutch is standard equipment on AMC machinery, and
spring loads range from 2000-2500 lb. The 304 clutch has generally used a 9-coil
setup, while the 360 and 390 have used 12 coils and three rollers, and the
newer 360 and 390 have used 12 coils and three rollers, and the newer 360 and
401 engines use 12 coils and six rollers. This last one is the unit recommended
for limited performance work by the factory racing people, since it has an
upper limit spring rate of almost 2600 pounds. But the factory recommends any
of the popular 10’/2" B&B aftermarket replacements, and a spring
loading around 3000-3200 pounds.
The
Borg-Warner 4-speed transmission commonly known as the T-10 has been optional
with AMC cars for many years, and two versions have been used. The close-ratio
box, using 2.23, 1.77, 1.35, and 1:1 ratios is the more widely used, though in
1968, the wide ratio T-10-T was optional and is still available. Complete
transmissions must be ordered from Borg-Warner, but gearsets alone can be had
through AMC. It used ratios of 2.64, 2.10, 1.46, and 1:1. These two and all
other versions of the T-10, including the aftermarket Super T-10 will bolt
right up to the 4-speed bellhousings on any AMC V8 engine. Performance
Activities told us that the '68-’69 T-10-V transmission used with 390 engines
incorporated a larger front bearing cap (3185168) and a bigger throwout bearing
(3190517) that should be installed on any later T-10 used for performance work.
Final selection of ratios would naturally depend on rear ratio, tire size, car
weight, and the extent of engine modifications, but there are so many B-W T-10
trans-missions around that there should be no problem in finding an ideal unit.
Gremlins, which don’t come with 4-speeds behind their 304’s, will accept a T-10
if the Javelin/ AMX trans mount is used and the driveshaft is cut 1.280".
The 4-speed bellhousing must-be used, though.
When it
comes to automatic transmissions, all but 1972 AMC cars used a Borg-Warner
three-speed with ratios of 2.40, 1.47 and 1:1, with 11" converters for 290
and 304 engines and 12" converters for 360, 390, and 401 engines. For
1972, the corporation switched over to Chrysler Torqueflite transmissions with
standard 2.45, 1.45, and 1:1 ratios and a whole lot more good features and
strength. The Chrysler-supplied transmissions use 10.75" converters for
304 engines and 11.75" units for 360 and 401 engines. The big hitch in
converting an engine that used the Borg automatic over to the Chrysler is that
the crankshafts must be changed to 1972 cranks with the proper flange thickness
and hole patterns to accept the Torqueflite flex plate on the flange. The stock
Borg transmission is flatly unacceptable for strenuous use, and the Chrysler is
just about the best available, especially since the aftermarket is loaded with
possibilities for shifters, converters, and valve bodies compatible with street
and drag strip use. Once the '72 Torqueflite (AMC still calls it Torque
Command) is installed, all that's needed is the '72 driveshaft for the
particular body style, since the Chrysler trans is shorter overall than the
Borg-Warner.
When it
comes to rear end ratios, American Motors has one of the best option lists in
the business, and they’re all built around the standard Dana rear with a basic
8.9" ring gear diameter. The 3.91 rear is 4485750; the 4.10 unit carries
number 3208546; the 4.44 ring and pinion set is number 3209854; the 5.00:1
screamer is listed as 4486587. All of these rears and in fact all AMC rears
from 2.37:1 on up are available with the four-pinion Twin-Grip option and
they’re as near bulletproof as they can be without modification or substitution
of aftermarket heat-treated ring and pinion sets. One of the parts that has
been trimmed from the "available" list is the 4486997 Detroit Locker
locking differential. It can't be had through normal AMC channels, but there
are undoubtedly a few used ones around at American Motors specialty garages.
That,
in a large nutshell, is the story on parts interchange possibilities, factory
available pieces, dealer-installed options, and AMC recommendations on building
relatively mild street and strip cars. We won’t get into suspension and
accessories, since there are so many variables involved, but we have taken you
through the entire engine and driveline and hopefully we’ve covered the basics.
AMC's Performance Activities Department is busy right now on the preparation of
a complete parts and procedures manual for all AMC cars and engines, and
they’re opening up an information service (letters only, no phone calls,
please) that will be invaluable to all AMC floggers. Direct all correspondence
to AMC Performance Activities Department, 14250 Plymouth Road, Detroit, Mich.
48232, and be specific in your letter as to car, year, engine, trans, rear,
class or intended use. After spending most of a week talking with the staff we
know you'll get a prompt, accurate, and complete answer to your specific
questions.