History: Gen 2 and Gen 3 AMC V-8s (1966 – 1991)

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High-Performance Engines from an Economy-minded Company

Surprisingly, AMC had always been in the high-performance game, even before the introduction of the GEN-1 V8. With the merger of Hudson and Nash in the mid-fifties that formed American Motors, AMC inherited Hudson’s racing heritage. Thus, it was no surprise that the original Rambler Rebels of the ’50s and early ’60s had some serious go. For more information on the GEN-1 engine program, see AMC GEN-1 V8 Engines 1955 – 1966.

By 1964, the old GEN-1 engine was an aging design. New V8 engines from almost every manufacturer were introduced in the mid-1960s. Engineering advances in casting and lessons learned in volumetric efficiency (read cylinder head design) that were learned in the racing programs that all the Big Three factories had been involved in during the late 50s began to be applied at this time. Also, the push for economic resiliency from the recession in the early 60s had resulted in a quest for lighter engine weight as well, so even as America went back to its thirst for large cubic inch V8s, the public demanded more power per specific engine volume weight – and better designs that made more horsepower.

Thus, even the smaller American Motors had to come up with a replacement for its aging V8.  The fact that they were a smaller company that had pioneered efficient cars worked in its favor. Best, they were able to evaluate the best of the Big Three designs and take the best approaches that had surfaced.  Among those were the Chevy Small Block, the Ford 260-289, and the Chrysler 361-440.

Because the Company had fewer resources and tooling dollars, AMC’s new engine was designed to be able to span what we call “small block” to “big block” displacements yet keep to a compact footprint, running in its lifetime from 290 cu. in. all the way to 401 cu. in., and with a capability (never used in factory production) to go to over 450 cu. in.

Enter the 290

The GEN-2 engine offered some great potential when AMC introduced it in 1966 as a small 290 cu. in V8 – available in the Rambler and Rambler Rogue compact. The engine features a bore of 3.75″ and a stroke of 3.28″, with a modern, lightweight valve train and compact overall design.  It was lighter than a Chrysler 273 and almost the same as the Ford 289. This 290 V8 only hinted at its performance possibilities when it was placed in a total of 625 lightweight Rogues in 1966. It had good power, modern cylinder heads, and a compact and lightweight design, and engineers told the press and the motoring public that it could be expanded to close to 400 cu. in. to easily to meet the power requirements of the Rebel and Ambassador.

In 1967, the 290 was made available with either a two- or four-barrel carburetor, this made equivalent power to the 283 Chevy and 289 Ford and showed equal or better acceleration. Its thunder was quickly stolen, however, by the introduction of the 343 and 390, who, of course, made much better power in the same sized and weight package.

An Upgrade to 343 Cubic Inches

Later in the year, a 343 cubic-inch version was introduced, ostensibly to power the larger AMC vehicles.  They had a 4.080″ bore and the 290’s 3.280″ stroke.  It made 235 hp when fitted with a 2-barrel carburetor and 280 hp when equipped with a 4-barrel.  (AMC was notorious for rating their engines with all accessories attached, this engine would have been rated at over 300 if it were introduced by Ford or GM).  When the 280 hp version was placed in the Rogue and Rebel, cars that were easily 500 lbs. lighter than their rival equivalents, AMC suddenly had a series of Muscle Cars.

Serious Cubes – the  390

The introduction of the Javelin and AMX in 1968 coupled with the expansion of the 343 to 390 cubic inches, made sure AMC would be highly competitive in the performance market.  The engine was enlarged by increasing the bore to 4.165″ and the stroke to 3.574″.  Amazingly, adding 100 cubic inches kept the block deck height and all other physical engine dimensions the same as that of the 290! 

This engine was again conservatively rated at 315 hp.  The torque figure of 425 hinted at its true potential. 390 equipped AMXs could run with the best Detroit had to offer, with only the 427 Corvette as a superior performance machine. AMC was also smart to offer aftermarket intake manifolds, camshafts, and other performance parts right alongside their own internal pieces, giving them factory part numbers, and ensuring competitive power for little added manufacturing cost.  Best, because of the engine design, all components fit all three engine sizes, letting the 290 and 343 owners reap the benefits of the 390’s popularity with racers.

For a small company, AMC’s smart decisions had leaped their engine development to be equal to or ahead of the Big 3 in engine design.  All this with a small investment, but an excellent strategy.

Comparative Size, Dimensions, and External Specifications

The table below shows the Gen 2 and Gen3 engine external specifications and weights, beginning with 1966 290 V-8 and including all low and high deck blocks, and ending with the 401 V-8. Below is a picture of how to measure to determine and identify the engines.  Also enclosed is a chart showing the size and weight of the engines and how to determine the dimensions from the enclosed picture.

AMC Engine Dimensions

Engine Displacement A Length B Length C Height D Height E Width Distributor Sump Started Oil Filter Average Weight
AMC Gen 1 250/287/327 Varies 27.75 24 Varies 24.12 rear rear right left rear 601/651
AMC Gen 2 290/343/390 28.5 29.25 20.75 29. 21.25 front rear right right front 540/600
AMC Gen 3 304/360/401 28.75 29.25 21.75 29.5 21.50 front rear right right front 545/605

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