From 1961 through 1963, Chrysler tried an aluminum-block version of the Slant 6, but we can’t exactly call it an experiment as more than 50,000 were produced.
From its introduction in 1960, it was clear the Chrysler Slant 6 was designed for compactness. The cylinder block was laid over 30 degrees, used four rather than seven main bearings, and the water pump was offset to the side to create the smallest possible package. (See our feature here.) Less well known is that the Slant 6 was designed for lightness. From the beginning of the program in early 1957, both cast iron and aluminum cylinder blocks and heads were developed, and the cast-iron version was declared ready for production with the launch of the 1960 Valiant. The aluminum block, a more difficult engineering task, came along one year later with the 1961 Dodge Lancer.
Both sand-casting and diecasting techniques were tried in the development of the aluminum block. (Due to its greater complexity, the aluminum head was abandoned early.) For its expertise in casting aluminum, the task was assigned to Chrysler’s Kokomo, Indiana transmission plant, where a high-pressure diecasting method was developed using SAE 303 aluminum alloy with 4.5 percent copper and 10.5 percent silicon in a dedicated 2,000-ton diecasting machine.
While the aluminum cylinder case was dimensionally identical to the cast-iron version with the same distributor, fuel pump, and water pump locations, etc., it was in fact a completely different design with an open deck to suit the casting process (above) and iron cylinder liners cast in place. A special laminated head gasket was required to mate the wet-deck aluminum block to the cast-iron cylinder head, using layers of steel, asbestos-rubber, and copper, torqued in place with longer head bolts to reach deeper into the aluminum casting. In service, the head gasket arrangement proved to be a weak point.
Another novel feature of the aluminum block was its cast-iron upper and lower main-bearing caps (above). Previous experience informed Chrysler engineers that iron’s greater dimensional stability throughout the engine’s temperature range made it worth the trouble. Chrysler originally intended to produce the aluminum-block Slant 6 in both the 170 and 225 cubic-inch versions, but ultimately chose to concentrate on the 225 CID block with its one-inch taller deck height to accommodate a 4.125-inch stroke.
Published estimates vary from 40,000 to 60,000, but it appears that 50,000 to 52,000 Chrysler products were produced with the aluminum block, mainly Dodge Lancers and and Plymouth Valiants. While the weight savings was significant at 76 lbs, Chrysler production engineers determined by late 1962 that the lightweight diecast block could not be manufactured at a sustainable rate or cost. The program was then cancelled, though a few early 1963 vehicles were assembled with the aluminum block. For the next 28 years and 12.5 million engines, every Slant 6 featured a cast-iron block.
Some irreverent memories:
1.) Many years ago when gas/service stations still existed, I worked at one which was across the street from a college. A coed drove in, and while her car was being fueled, she asked to have the oil checked. I opened the hood, threw my hands up to my face, feigned a horrified look, as the poor girl leapt out of the car and asked “what’s wrong”? Pointing, I said “Look! Your engine tipped over”! “Oh no”, she said, “I better call my dad”!
2.) When in the Air Force, we employed “tugs” (small tractors) powered by six cylinder engines, some of which were Chrysler slant sixes.
3.) Visiting relatives in Alexandria, VA, I was invited to partake of Thanksgiving dinner aboard a U.S. Air-craft carrier docked in Norfolk, VA, we were taken on an “unofficial” tour of the ship, and on the hangar deck were greeted by two sailors engaged in a drag race involving slant six powered tugs.
4.) A neighborhood buddy had a Dodge A108 van, powered by a “Hyper Pak”
slant six, and he would race anything else – no matter what – and surprised a lot of other drivers.
5.) Driving my cousin’s slant six Valiant on an interstate, when a Corvair issued a challenge, I was determined. I said “I’ll blow this thing up before I let that Corvair beat us”! Instantly sanity returned. I remembered, it’s not my car; it’s my cousin’s, and he’s sitting in the passenger seat.
The slant six stood the test of time. It was one of the most indestructible six cylinder engines ever built. The aluminum version would have been better if it had an aluminum head.
In 1973 my cousin and I decided to build a machine to compete in the mini-modified classes of the North Carolina Tractor Pullers Association. A mechanic friend offered us an aluminum block slant six that we used to win the 1974 NCTPA championship in both weight classes, competing against mostly small block V8 Chevy and Ford machines. The thing was amazing!