Want sick power from a basically stock engine? Try a 401. Using
factory heads on the portly 4.170-inch bore,
you can build torque where it counts and still make good power on top with a reasonable cam, good vacuum, and off-the-shelf parts.
In the case of the buildup we're outlining here, the payoff was 484 hp at a street able 5,600 rpm and nearly 500 lb-ft of torque at 4,600,
with more than 450 lb-ft from 2,500to the horsepower peak.
With the help of JT Payton at Payton's Performance, Holley
Marketing Manager Bill Tichner did all of that. His goal for the 401 was
use as many stock parts as possible and create as much power as possible while still maintaining at least 13 inches of vacuum for an
aftermarket fuel injection system to come later. The performance key to this engine is heavy port work on the iron heads, attention to the
oiling system, and a couple of other tricks we will outline in this story. This engine's destiny is to be stabbed into an AMX, and with a little
shot of spray, lift the wheels at its favorite track.
The practical limit of the plebian AMC 401 is about 500 hp at 7,500
rpm. The main caps will begin to walk above that, so limit these
engines to healthy street mills if you want to keep the price down and use stock parts. Just because we're interested in this kind of thing,
we found that with an available four-bolt main kit, you can go to 700 hp and9,500 rpm for the full-race Chihuahua. Whee.
But this is a street engine, so Tichner used a post-'70, tall-deck block bored 0.030-over for4.195 inches and used the stock two-bolt
main caps with big-block Chevy studs from ARP.
We'd recommend using the stock bore if you can. Payton's says the
high nickel content in these blocks makes them resistant to wear,
and0.030-over is on the limit of the 401's block design. So if you don't have to bore, hone it and move on.
The Rotating Assembly
Lots of goodness here. The stock rods and crank on all AMC 390 and
401engines are forged from the factory. To keep them working,
Payton's shot-peened the stock 5.85-inch rods to relieve stress and used a pressed piston pin for street durability and low bucks.
For full-tilt mills, Payton's uses a 6-inch Chevy rod and turns the rod-bearing journal down to 2.100 inches from the stock 2.248 for
reduced cylinder-wall loads and 7,500-plus-rpm capability. Taking no chances, they use ARP rod bolts as well.
The 401 crank has a 3.68-inch stroke and is more than manly enough
with just a polishing of the journals and chamfering of the oil holes
to live. It's worth mentioning that the '72-and-later 401 crank had a Torque Flite 727 flange, so look for the casting number 812-0510 or
you will have to modify the flange to get it to work with a modern automatic.
We asked a couple of builders about off-the-shelf pistons and got
head scratching and thinking but no part numbers. This engine uses
a custom Lunati aluminum-alloy forged flat-top for future use of race gas and nitrous. At around $640, it is the most glaring expense on
this engine. The slugs have a 1.48-inch compression height with two 17-degree valve eyebrows spaced 1.590 inches apart with a
total of 11.23 cc's of relief. With a 0.043-inch thick gasket, 0.020-inch deck clearance, and the 64ccheads they're good for 10.0:1
There are Indy and Edelbrock heads available for the AMC, but
Tichner wanted to use the stock dog-leg heads. The cork in their
design is the intake runner and the exhaust-port-to-header match. Payton's put in about 11 hours of work to cut the stock valve seats
and fit a set of2.08 intake and 1.625 exhaust valves and raise the intake runner. ayton's machinists are careful to avoid the intake floor,
because past experiments found that changes there actually hurt airflow. Extensive work in the combustion chamber was performed
to unshroud the valves and open the chamber from 58 to 64 cc's. This was also helpful in reducing the compression on this engine to
run on pump gas. The final flow numbers were 279/210 cfm at 0.700-inch lift at 28 inches of water. Those re big ports for a cast-iron
On the exhaust side, the rough casting was cleaned up and the
headers were port matched to the heads.
Early Super Comp 17/8-inch full-length headers for the '68-'74 Javelin/AMX and '74 Matador need to have the flange opened
up a bit to match the exhaust port, but new headers of his design should already be modified to fit.
Carb And Ignition
This engine was built with the future installation of Holley's
Commander950 MPFI kit in mind. It has a single-plane manifold and
throttle-body cluded. For the dyno run, Tichner used a manifold that is similar in design from Herman Lewis Racing and a 950-cfm Holley
HP Series mechanical-secondary carb. The cfm might seem a little much, but this engine is going into a light AMX that will likely see
more WOT on the track with a plate of nitrous than street cruising. According to Payton's dyno sheet, the A/F ratios were correct for this
size carb on this combination.
MSD offers both a standalone ready-to-run distributor and the
Pro-Billet that requires an MSD 6-, 7-, 8- or 10-series ignition to
Both come with a vacuum advance and replace the stock points stuff. Tichnerchose the Pro-Billet and a set of Autolite AR52 racing
plugs to spark it all.
Cam and Valve train
The cam was a sacrifice to get some vacuum at a loaded idle. It is
a Lunati hydraulic flat-tappet grind with 230/235 degrees of duration
at0.050, a valve lift of 0.0523/0.0540, and 108 degrees of lobe separation. The full-kill cam is also a Lunati grind, but it uses a solid lifter
and has 249/259 degrees at 0.050 and 0.579/0.598 lift with the same lobe separation angle. It will sacrifice more idle quality and
vacuum but would likely crest 500 hp on this combination. The rocker arms are aluminum rollers made for a Ford 260-351W but
useable on the090 and 993 castings with Lunati springs with 105 pounds of seat pressure at 1.80-inch installed height.
Ultimately, the engine is destined for Tichner's AMX. We'll let him
"I bought the car from JT (Payton) when I was 17 and drove it
daily through five years of college. Then I joined Holley in 1994 and
it for a year until I was able to afford a more dependable car (with A/C, fuel injection, and better gas mileage). I have been driving the
car as-is as a toy since marriage, a home, and kids took all my income. Now after 10 years at Holley I am able to really start working on it.
The bodywork has just been finished and the engine compartment is painted. It is going to be Pepper Grey Metallic with black Go Pack
stripes. Once I put everything back in the engine compartment, it's going back for paint. I have a Torque Flite 727 that I got with the 401
out of the donor'73 International Travel-all, but I am not sure if I will build it or something else at this point. I still need to build the rear end
to handle the power as well. I know I want 3:55 gears and probably a 2,500stall since the torque comes on immediately from this motor.
The car was originally a 390-cid car. I bought it with a 290 and then put a high-compression 360 in it during college. Now it has the 401.
I am going with the multipoint EFI so the factory hood will be able to close.You can't get this kind of power out of an AMC and keep it
under the stock hood with a carb."
Tips and Tricks
It's no secret that the AMC V-8 has a failing in its lubrication
system. Oil from the pickup travels through a passage on the oil-pan rail
a pump with an aluminum housing that tends to wear, then to the filter, and finally to the main oil galley. It's nowhere near good enough
for even a stocker, in our opinion. The solution is the Milodon single or dual pickup that bolts directly (and conveniently) to a
Milodon deep-sump oil pan. It bypasses the stock restriction and nearly doubles oil flow to the filter and mains. Payton's adds a filter
before the oil reaches the pump gear in conjunction with a direct-oil feed from the main galley in the lifter valley to the rear main bearings,
because on a stock AMC, they're the last in line and tend to fail during high-rpm use.
Stock AMC oil-filter adapters are made of aluminum, and the pump-gear face rides directly on the housing and wears it down. Fortunately SpeedPro sells a replacement kit for the oil-pump gear assembly and pressurespring, and we've seen the 340/360 Mopar service replacement housingbeing used for 390/401 performance applications, so look to Jeeps forthis part.
|Payton's Performance AMC Engine Build Specs|
|Main bearings||Speed Pro||4950 M|
|Rod bearings||Speed Pro||8-3385CP|
|Rings||Speed Pro||R-9349 35|
|Oil pump||Speed Pro||224-51285|
|Cam bearings||Speed Pro||1401 M|
|Head gasket||Fel Pro||8266PT1|
|Intake||Herman Lewis Racing||call|
|Spark plugs||Autolite||AR52 Racing|
|Valve covers||Payton's Performance||call|
|Oil line to rear main:|
|3/8 NPT to 8-AN, straight||Earl's Performance||820108ERL|
|3/8 NPT to 8-AN, 45 deg.||Earl's Performance||824508ERL|
|Perform-o-Flex hose||Earl's Performance||403008ERL|
|Holley Performance Products
1801 Russellville Rd.
Bowling Green, KY 42101
2700 California St.