The Duesenberg J is often described as the greatest straight-eight production engine the United States has ever produced.

When industrialist E.L. Cord acquired the Duesenberg Automobile & Motors Company of Indianapolis in October of 1926, he famously gave brothers Fred and August Duesenberg a simple direction: Produce the finest automobile they knew how to make.

When the resulting product, the car that became known as the Model J, debuted in New York on December 1, 1928, it was a tour de force in a number of ways, but its centerpiece was the engine: a highly advanced straight eight that reflected decades of Duesenberg racing experience, including three Indianapolis 500 victories. The engine was rated at an astonishing 265 hp at 4200 rpm—more than twice the output of a  Packard or Cadillac, the USA’s luxury-car leaders that year. The Model J offered power on another level.

Designed by Fred Duesenberg in Indianapolis, the J engine was manufactured by Lycoming Foundry and Machine Co. of Williamsport, Pennsylvania, also part of the E.L. Cord empire and the producer of engines for Auburn and Cord as well. (Reportedly, the  Duesenbergs were perpetually dissatisfied with Lycoming’s production standards.) With a bore and stroke of 3.75 inches by 4.75 inches, the big undersquare straight 8 displaced 419.7 cubic inches.

The block and cylinder head were cast in chrome-nickel iron, while the cam cover, timing cover, oil pan, and bell housing were cast aluminum. On the bell housing was stamped the famed J number—the letter J followed by a hyphen and three digits, by which Duesenbergs are traditionally identified (though they have chassis numbers as well).

Duesenberg advertising called the Model J’s crankshaft its “backbone.” Forged in chrome-nickel-manganese alloy, it was 42 inches long with eight fully counterweighted rod journals 2.75 inches in diameter, and it weighed a husky 150 lbs in finished form. Fastened to this long, massive chunk of steel between the first and second rod journals were two capsules (not shown) partially filled with 16 oz. of mercury each to dampen the formidable torsional vibrations of eight inline cylinders. Crank phasing was the two-plane pattern introduced by Packard in 1924 (see our feature here). In the Duesenberg parts catalog, the crankshaft listed for $605, the price of a new Model A Ford at the time.

The camshafts and accessories were driven from the crank by a pair of heavy three-row chains and sprockets, while the Delco dual-point distributor was driven from the left (intake) camshaft. In an interesting twist, the 9.8125-in long connecting rods were forged in Duralumin aluminum-copper alloy with steel caps, while the pistons were Duralumin as well. Total engine weight was quoted as 1,150 lbs.

The heart of the straight 8, and the key to its impressive performance, was the double-overhead cam, 32-valve cylinder head layout developed from years of Duesenberg racing experience. In this aspect of its design, it was essentially a racing engine for the road. The cam lobes acted directly on bucket-type followers, with two 1.5-in intake valves and two 1.4375-in exhaust valves per cylinder with .36 inches of net lift.  Simple yet sophisticated, the robust setup used the finest materials available, while the pentroof combustion chambers supported a compression ratio of 5.2:1.

Duesenberg scholars have debated the accuracy of the official power figures for the Model J, many theorizing they are probably overstated. In his book The Classic Twincam Engine, noted author Griff Borgesen offered that Lycoming’s 265 hp rating might be closer to 209 hp, and as you can imagine, there are a whole range of opinions on the matter. Whatever the numbers, the Model J’s output was at least the equal of any production car on the road in its time. Between 1929 and 1937, there were relatively few engine revisions. In 1934, the carburetor was updated from the original updraft type to a more modern downdraft two-barrel.

Following the rule that too much power is never enough, in May of 1932 Duesenberg once again tapped into its racing expertise and offered a supercharged version of the J, known as the SJ (below). A Switzer-Cummins centrifugal blower with a giant 12-inch impeller on the right side of the engine ran at six times engine speed, producing up to 8 lbs of boost. In this form the engine was rated at 320 hp at 4750 rpm—a figure that wouldn’t be exceeded by an American production car for several decades.