(Thanks to Stephen Havens)
All horsepower ratings before 1970 are gross measurements (without accessories and such). Ratings after 1971 are net measurements and are lower even for the identical engine.
The A engine was produced from 1955 through 1966. The LA, introduced in 1964, had the same basic design but was very heavily modified. The lightweight ("L" A) or thin-wall casting and heads saved around 50 pounds; the wedge-shaped combustion chamber was much smaller than the A engines’ poly heads, greatly reducing the size and allowing the first LA engine (273 V8) to fit into the small Valiant. The LA's valves were simpler too, saving money and size. The 273 ended up being only fifty pounds heavier than the 225-cid slant six.
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