Chrysler IV-2220 / XI-2220
Chrysler had been carrying out paper studies of a very large engine for a brief period starting in May 1940 and decided to present their work to the United States Army Air Corps. They proposed a large engine to provide 2,500 hp initially, with room for growth upwards. They had decided to use a larger number of "normal sized" cylinders in a V-16 arrangement. The Army was interested, and sent them a development contract tender on June 22, 1940, to which Chrysler responded on July 2.
A single overhead cam drove the two-per-cylinder poppet valves, arranged at an angle to the piston in a hemi-spherical cylinder head, with the spark plug arranged between the valves. This arrangement allowed for "cross-flow" scavenging of the charge, and had been used on various race and performance car engines for some time. The hemi is actually less efficient than the design being used in most engines of the era, the penta engine, which improved airflow by allowing three or four valves per cylinder.
One early problem for the design was the lack of high-strength aluminum alloys; the original supplier, Alcoa, was able to deliver only half the required strength. Chrysler was able to address this through much improved production-line quality control, but the engine was nevertheless built with considerably more distance between the cylinders than normal, making the engine relatively long. This was not helped by the "gap" holding the propeller gearing in the middle of the engine, or the large accessories section at the end. The IV-2220 was comparatively huge; the Rolls-Royce Griffon of about the same displacement was 77 inches long, while the IV-2220 was 122.
Weight was not greatly affected, however, and the power-to-weight ratio was certainly competitive at 1.03 hp/lb. Some of this was no doubt due to the use of a turbocharger in addition to a supercharger for more continuous boost and less power draw on the engine. Turborchargers are generally "free," powered not by the engine directly as in a supercharger, but by otherwise wasted exhaust energy. The IV-2220 also included a fairly advanced liquid-cooled intercooler between the turbocharger and supercharger, and an aftercooler behind the supercharger as well. This complex arrangement resulted in excellent altitude performance, keeping maximum rated power all the way to 25,000 ft.
The engine first flew on 26 July 1945, mounted on a converted P-47D-15-RE which was intended to serve as the prototype for the new P-47H series using this engine. A second example followed, but the war was already over and the need for a new engine in the jet age was gone. The only other design to select it was the Curtiss XP-60C in 1942, but the engine was so delayed that the P-60 moved onto other engines.
Only a few engines were built during the program, and it retained its 'X' designation the entire time as the XIV-2220, later XI-2220. The IV-2220 is historically important as it was Chrysler's first hemi, a design that would re-appear for many years later and is now a Chrysler trademark.