Simple, tough, and reliable, the four-cylinder Model A engine powered more than five million Ford cars and trucks.

Proudly aware of his place in history, Henry Ford enjoyed recording his major moments for posterity. Here he’s shown punching the serial number A1 on the first Model A Ford engine to exit the line on October 20, 1927. The official introduction of the new car to the public would come on December 2. While a replacement for the Model T was seriously in the works by the summer of 1926, it became a crash program on May 26, 1927 when the founder shut down Model T production while the new car was prepared for market.

While Ford himself was less personally involved in the development of the Model A than in previous products, he hovered over every decision. Laurence Sheldrick and Harold Hicks were chiefly responsible for the engine, working closely with production bosses Charles Sorensen and Peter Martin. Sheldrick, a Lincoln veteran, eventually took charge of the entire Model A project. However, the man responsible for the style, colors, and presentation of the new product was Edsel Ford.

While the Model A engine was similar in general configuration to the Model T’s, with a cast-iron block, detachable head, L-head valvetrain, and manifolding on the right side, no parts interchanged. In fact, the Model A was considerably larger in displacement at 200.5 cubic inches, with a 3.876-in bore and 4.125-in stroke. Originally, the bore was to be 3.75 inches, but ultimately they reasoned that an extra 13 cubic inches couldn’t hurt.

Unlike the Model T, which relied entirely on thermo-siphon cooling, the Model A incorporated a belt-driven water pump as well. Also, the A discarded the antiquated low-tension magneto of the T in favor of a conventional breaker-point distributor. However, there was no fuel pump, as the carburetor was gravity-fed from the fuel tank in the cowl. As always, the founder was obsessed with simplicity and minimum component count. The oil system was a combination of pressure, gravity, and splash, while the compression ratio was a conservative 4.22:1.

From the start, 40 horsepower was selected as the output target, compared to the 20-22 hp of the Model T. But in initiial dynamometer testing the engine fell far short of the objective, producing little better than half that. Hicks addressed the power shortfall with improvements to the valve timing and manifolding. According to Sorensen, Edsel Ford spotted a deficiency in the intake manifold that uncovered a significant gain in power. Ready for production, the net result was 40 hp at 2,200 rpm and 120 lb-ft of torque at 1,000 rpm. With only 2,200 lbs to push around, the Model A was known for its jack-rabbit starts, and in decent tune it could run 60 mph, more than sufficient for the roads of the time.

Like everything else about the Model A engine, the carburetor was a model of simplicity. A single-throat updraft unit with an .846-in venturi, it featured a bare minimum of  adjustments. While the Zenith Carburetor Company of Detroit was the primary manufacturer, Holley and Tillotson were suppliers as well. In Model A lore, it’s said Henry Ford repeatedly rejected the Zenith carburetor design, saying it used too many screws. When the frustrated Zenith representative finally produced one with a single through-bolt holding the upper and lower castings together, he approved it.

Not quite five million Model A Fords were built over the 1928 to 1931 model years, roughly a third of the Model T’s production total. But in that time the Model A’s four-cylinder engine earned the same reputation for ruggedness and willingness to withstand abuse. There was a Model B engine, too, a mildly upgraded version of the A offered in 1932-34 alongside the V8. Miller, Cragar, and others produced overhead-valve and overhead-cam conversions for the A/B engine, which powered dirt-track racers all through the ’30s and ’40s and helped to launch the hot-rod movement.