Chrysler built more than 50,000 cars with an aluminum-block Slant 6 before production challenges brought the project to an end.
From 1961 to 1963, Chrysler experimented with an aluminum-block version of its Slant 6 engine. Calling it an experiment might be misleading, though, since more than 50,000 vehicles were reportedly built with this unusual powerplant.
When the Chrysler Slant 6 debuted in 1960, its compact design was immediately apparent. The engine's cylinder block was tilted more than 30 degrees, it used four main bearings instead of seven, and its water pump was offset to save space. Less widely known is that engineers also designed the Slant 6 with weight reduction in mind.
From the beginning of the program in early 1957, Chrysler engineers considered both cast-iron and aluminum blocks and cylinder heads. The cast-iron version debuted alongside the Plymouth Valiant in 1960. The more challenging aluminum block arrived a year later in the 1961 Dodge Lancer.
Chrysler explored both sand casting and die casting to produce the aluminum block. An aluminum cylinder head proved too complicated and was abandoned early in development.
Responsibility for the project went to Chrysler's Kokomo, Indiana, facility, which specialized in aluminum casting. Engineers developed a high-pressure die-casting process using SAE 303 aluminum alloy containing 4.5% copper and 10.5% silicon. The process required a specialized 2,000-ton casting machine.
Although the aluminum block matched the cast-iron version's external dimensions, including the locations of the distributor, fuel pump, and water pump, its internal construction was substantially different. The casting was redesigned for the manufacturing process and used cast-iron cylinder liners.
Connecting the aluminum block to the cast-iron cylinder head required a specially designed laminated head gasket. It consisted of layers of steel, asbestos-based rubber, and copper. Longer head bolts were also needed to extend farther into the aluminum casting.
In service, however, the head gasket proved to be a weak point in the design. The combination of different materials and the demands of sealing the engine created challenges that complicated the aluminum version's long-term durability.
Another distinctive feature of the aluminum Slant 6 was its cast-iron upper and lower main bearing caps.
Chrysler engineers had learned from previous experience that cast iron maintained its dimensions more consistently across the engine's operating temperature range. They considered that added stability worth the extra manufacturing effort, even in an engine designed primarily to save weight.
Chrysler initially planned to offer the aluminum Slant 6 in both 170-cubic-inch and 225-cubic-inch versions, equivalent to approximately 2.8 and 3.7 liters. The company ultimately concentrated on the larger 225-cubic-inch engine.
Published production estimates range from 40,000 to 60,000 vehicles. The most widely cited figures suggest that approximately 50,000 to 52,000 Chrysler vehicles received the aluminum-block engine, primarily the Dodge Lancer and Plymouth Valiant.
The weight savings were substantial. The aluminum block reduced engine weight by about 77 pounds compared with the cast-iron version.
Despite that advantage, Chrysler's manufacturing engineers concluded by late 1962 that the lightweight casting could not be produced quickly enough or at a competitive cost. The program was canceled, although a small number of early 1963 vehicles were still assembled with aluminum-block engines.
The decision marked the end of Chrysler's effort to bring this lightweight Slant 6 into broader production. Over the following 28 years, approximately 12.5 million Slant 6 engines were produced, and every subsequent version used a cast-iron block.
The aluminum Slant 6 remains an unusual chapter in Chrysler's engineering history: a production engine that delivered meaningful weight savings but proved too difficult and expensive to manufacture at the scale the automaker needed.