The original Hemi V8 debuted on the 1951 Chrysler and then moved out to Dodge and DeSoto cars; Plymouth never had one because at that point Chrysler, Dodge, and DeSoto were strictly upscale and Plymouth was mass-market. To make a V8 practical for Plymouth, it had to be cheaper and faster to make—much cheaper, much faster. Indeed, just to keep up with demand for V8s in Dodges and DeSotos, the company had to simplify the dual-rocker hemispherical heads, which led to the “poly” V8s—single-rocker polyspherical-head engines.
The first Chrysler V8s meant to be truly mass-produced, the “A” engines, debuted in 1955, re-engineered somewhat for more automated assembly in the then-state-of-the-art Mound Road plant. They, too, had polyspherical heads; the company still insisted that the design, while not as efficient as hemispherical heads, allowed for higher compression and cleaner burning. It also allowed for a cross-flow design for better breathing. Engineer Pete Hagenbuch, after his retirement as head of production engine tuning and, later, emissions, said that the design was supposed to keep the Hemi’s benefits, but at a much lower cost.
The problem with the original Chrysler V8s, other than cost, was that they had a maximum displacement built in; the largest ones ever made were the famed 392s. The engineers were told to set up a brand new V8 engine design that would be larger, cheaper, and faster to build; these ended up as the B and RB engines, which included the famed 426 Hemi, the workhorse 383, and the 413 and 440. While they were creating them, the engineers tested numerous types of combustion chamber design, which they had not done since creating the original Hemi; they found, to their surprise, that the conventional wedge chamber used by their main competitors was as good as the polysphere. With that, they dumped the pricey polyspherical chambers and switched to wedges.
Meanwhile, they had to create a small new V8 engine option for new Barracuda, a sporty version of the Valiant; the engine bay was too small for their big A-engines, and it would make the car unwieldy to have all that weight up front anyway. The engineers used a new lightweight casting method, switched the heads from poly to wedge, and thus created the new LA series engines—an engine family which would continue all the way into the 21st century and be adapted into V6 and V10 formats. The first LA engine was a little 273; unlike its predecessors, it had spark plugs that could be changed from above, which was rather handy. It went into the 1964 Plymouth Valiant Barracuda, and in the next year was the standard V8 in midsize Dodge and Plymouth cars. A four-barrel version with a hot cam could move the light Barracuda to 60 mph in just 9.1 seconds, with a whopping 235 bhp and 260 lb-ft of torque. (Brake horsepower numbers are gross figures, without engine accessories, and cannot be directly compared with today’s net readings.)
The next step was regaining the 318 cubic inch displacement from the A engines by making a larger-bore version of the 273; that was phased in during 1967 and 1968 in the US and Canada, causing a great deal of confusion but saving money on tooling. Versions of the LA would reach 340 and 360 cubic inches; the 340 was only ever used for high performance, but they made both low and high performance 360s.
The LA served with distinction for many years; though the last cars with that engine were 1989 models, they continued on in trucks, gaining fuel injection and then having their “heads on up” completely redesigned to create the “Magnum” engine series. Displacement was the same—318 and 360 cubic inches, or 5.2 and 5.9 liters. The 318 was eventually replaced by the 4.7 V8; the 5.9, by the 5.7 Hemi. That was a worthy and ironic end to the LA series—created from the Hemi and eventually replaced by a new Hemi.