Evolution of The American Motors AMX – The Other American Muscle Car

The starting point for the AMX came when American Motors hired Dick Teague as assistant director of design in 1959. Three years later he became vice-president of Automotive Styling and a new era began at AMC. Teague’s job was to take American Motors from being a small economy car builder to a company more competitive, on a broad scale, with the Big Three (Ford, GM and Chrysler). Many historians say American Motors should have stayed with building only small cars, or at least small and midsize cars, and shied entirely away from building larger models, because Ford, GM and Chrysler owned that market segment.

In the end, perhaps nothing would have made a difference in AMC’s fate, but for one brief period in the late 1960s, America’s number four automaker managed to butt heads with Detroit’s Big Three and give them a run for their money with the AMX and Javelin.

AMX fiberglass concept car

The next step in the evolution of the AMX was the fiberglass concept car. This was a non-driving model for the auto shows. You can already see the final production AMX taking shape.

1970 model year AMX
For the 1970 model year the AMX got a facelift and a new, bolder hood. It seems odd that AMC would have gone to the trouble of changing the car for one year, but when the styling work was underway, it is possible that the car was planned for a longer production cycle.

The AMX concept was made from start to finish at the old Nash Motor Company (American Motors Corporation) facility at 14250 Plymouth Road, in Detroit, which was American Motors World Headquarters at the time. The AMX started from drawings done by a number of artists (about 20 men working full-time). Quite a few ideas were taken from Erick Kugler’s drafting table in January or February 1965. From there, Bill Mitchell and his men in the wood shop built a wooden platform for the clay model.

To save money, AMC made a two-seat sports coupe from the clay model of the production Javelin, changing only the grill, hood, door glass, quarter glass and roofline through different quarter panels. The four cars, the AMX II, the Javelin, and both the AMX show car and production AMX, were being made basically at the same time but in different studios.

American Motors AMX
The AMX first appeared as a 1968 model. In 1969 performance extras included a 140-mph speedometer and an 8000-rpm tachometer. Under the hood breathed a standard 290 cubic-inch, four-barrel V8, with 343 and 390 cid engines optional.

From 1971 to 1974 AMX was reduced to an option on the Javelin, and the Javelin itself was dropped after 1974. Actually the 1971-1974 cars handled the best; they just didn’t have the same appeal.

1971 American Motors Javelin
After being discontinued as a two-seat model in 1970, the AMX name reappeared in 1971 as an option for the 2+2 Javelin model.

In a somewhat less than glorious reprise, the AMX name returned in 1977 as an option on the AMC Hornet. In 1978 AMX was an option on the Concord. The last production AMX cars were made in 1979 and 1980 as an option on the Spirit. After that, there was a single AMX Turbo made out of house by Autodynamics of Troy, Michigan. John Starr did the original rendering and Dick Teague oversaw the project. The car was made for the PPG Indy Car World Series and was to be used as a pace car during the 1981 season.

The AMX is best remembered in its two-seat form, its true form, if you will. It was its lightest and fastest as a two-seater, winning many races on the quarter-mile drag strips across America, and on racetracks by Team AMX, a group of 20 AMC employees headed up by Jim Alexander. A total of 106 speed and endurance records were also set by Craig and Lee Breedlove, not to mention the times those few AMX cars that were in the neighborhood cleaned the clocks of the local bad boy Fords, Chevrolets and Mopars.

Today, the original two-seat AMX is receiving well-deserved recognition on various automotive television shows and in books and magazines around the world. The AMX has been featured in car calendars, on collector cards, in die cast models of different sizes, and the real cars are winning at top Concours d`Elegance events around the country. The AMX had a short but memorable existence.

By C.L. Zinn II on Friday, May 13, 2016 in 1960s, 1970s, AMC, AMX, Articles, Car Collector Magazine Edited version, for full text and and many more images go to https://heacockclassic.com/articles/evolution-of-the-american-motors-amx-the-other-american-muscle-car/
Portions of this article were excerpted from AMX PHOTO ARCHIVE From Concept To Reality and used by permission from Iconografix, Inc.

Read More Car Collector Magazine Articles

By C.L. Zinn II
© Car Collector Magazine, LLC. (Click for more Car Collector Magazine articles) Originally appeared in the January 2004 Issue

July 13, 2014 /by Randy for full text go to http://gremlinx.com/amc-myths/

A 390 cubic inch performance model was introduced for the 1968 AMX. This used the same dimensions as the 290 and 343 but had thicker main bearing webs for added stiffness in that area. AMC never produced a factory four bolt main bearing engine as they felt the two bolt cap was adequate, but they did cast the webs thick enough to be drilled for aftermarket four bolt main caps for racing purposes. To keep high reliability with the longer stroke all 390 and larger AMC engines used forged crankshafts and rods. According to AMC engineers forgings were originally used due to inadequate time to test cast parts. AMC decided to keep the forgings, either due to low numbers of the engines or to retain high reliability. In either case an AMC 390/401 is much stronger than comparable small block 400 engines. No aftermarket cranks or rods are required for racing, just careful preparation of the stock parts.

Displacements were increased in 1970 by lengthening the deck height of the block by 0.16″ for that much longer stroke. The 390 had built such a performance reputation that a new rod was made to keep a 390 for 1970. The stroke was changed only 0.11″ for the big engine to bring displacement to 401 cubic inches for 1971. It was felt that more than 400 inches would be larger than needed. Even then the block had to be notched at the bottom of the bores to clear the crankshaft counterweights. The higher deck height meant a slightly wider intake was necessary.

The heads were also changed in 1970. 1966-1969 heads have rectangular exhaust ports. 1970 and later heads have a “dog leg” or “pork chop” shaped exhaust port. The larger port increased exhaust flow by around 50%, making AMC heads the best flowing production heads available. For this reason the Chrysler “Magnum” V8 head was based on the AMC design. The new ports also required new exhaust manifolds.

AMC V8 engines are generally classified as GEN-1, GEN-2, and GEN-3 (GEN for generation). The GEN-1 engine is the large 1955-66 250-327 block, GEN-2 the smaller 1966-69 290/343/390, and GEN-3 the taller 304/360/401 (and 1970 390) model. Although the GEN-2 and GEN-3 share essentially the same block except for the 0.16″ deck height increase, the head, intake manifold, and exhaust manifold changes justify the separate designation. GEN-3 engines also use 1/2″ head bolts, GEN-2 uses 7/16″ head bolts. Heads will interchange between the two as long as the bolt size is accounted for. Step dowels are made to fit the better flowing GEN-3 heads on GEN-2 blocks, but for racing purposes it is better to drill and tap the older block for 1/2″ head bolts. To put GEN-2 heads on a GEN-3 block the bolt holes must be reamed to fit 1/2″ bolts.

Technically AMC didn’t build a small block or big block, they just made one V8 engine with the exception of the short overlap in 1966. In reality the engines are compared with the competition.

With this in mind the GEN-1 can be considered a “big block” because of its external dimensions and weight, and the GEN-2 and GEN-3 small blocks for the same reasons. Some publications have mistakenly called the 390 and 401 “big blocks” because of the displacements. Externally all GEN-2 and GEN-3 engines are the same size with the exception of height and width. All bolt patterns and external bolt on parts (except intake and exhaust manifolds) are identical. All internal parts interchange, though crankshaft and rod swaps may require custom pistons. GEN-1 parts are unique to that engine.

All 1970 and later AMC heads use the same port design. All 360, 390, and 401 heads are identical. These use 2.025″ intake and 1.680″ exhaust valves (early 70 used a 1.625″ exhaust valve) and have the high flow “dog leg” exhaust ports. If building an AMC race engine simply order pistons for the desired compression ratio and forget the smaller chamber heads — it won’t cost any more (maybe less!) if the pistons need replacing anyway. 1970-early 71 304 heads use a different casting (3199517) but are essentially the same as the 360/390/401 heads. Ports may be slightly smaller and castings a bit thinner, but according to all AMC technical data 2.02″/1.62″ valves can be installed. Combustion chamber volume for the 304 head is 52.20cc and produced a compression ratio of 9.0:1 with stock pistons. Later 304 heads have a 58.92cc chamber and produce 8.4:1 compression.

The bore size of GEN-1 engines is cast into the right rear of the block just behind the head. It’s in the space between the head and bell housing flange. This area is very hard to see with the engine in the car due to the close proximity of the heater housing. It may be viewable with the help of a small inspection mirror, and might need cleaning with a small wire brush. The cubic inch size of all GEN-2 and GEN-3 engines is cast into each side of the block just behind the engine mount plates in the center of the engine. Since the Engine Day Build Code or serial number is located on a removable tag this is the only reliable way to identify engine size. This does not apply to the Packard V8 engine.

An exception is the 1970 thick cast 360 used as a service replacement (SR block). This block could be bored and decked to build a 343, 360, 390, or 401. Dealers could therefore stock one part number to service four different engines. It can be identified by the lack of a displacement cast into the side. The casting number will be for a 401 engine. This block was used for racing as a thick walled 360, and in Trans-Am racing as a 5.0L. It MAY have been cast specifically for T/A racing at Mark Donohue’s request for a heavy duty block, but because it carried a standard AMC part number and was available across the counter to anyone, it did not have to be homolgated like the “Duck Tail” spoiler. The Donohue Javelin could be ordered with a 360 or 401. If the SR block had required homologation, it would have ben the only engine option. There is a machined pad just above the front left oil pan rail that usually has the built size stamped into it. Some builders/dealers used a code that has yet been undeciphered, possibly because they are not all the same, though partly because these blocks are relatively rare now. In this case the only way to verify displacement is to measure the bore and stroke. These blocks have been found in almost all AMC models, a few verified to be factory installed. Note that a SR block that has been bored out to 390/401 size is worth no more than any other 390/401 block — at that point that’s all it is.