Weird Warrior: Chrysler’s A57 30-Cylinder Tank Engine

Weird Warrior: Chrysler’s A57 30-Cylinder Tank Engine

Posted on April 20, 2017 by MCG

Necessity is the mother of invention, especially in wartime. Here’s one of the most unusual powerplants ever produced in the Motor City: the 30-cylinder Chrysler A57 tank engine of World War II. Let’s take a closer look. 

Despite some shortcomings, the Sherman M4 tank was a valuable tool for the Allies in World War II, and it was produced in vast numbers—nearly 50,000 units. One of the challenges was in building suitable engines for the 40-ton tank in sufficient numbers. The array of powerplants included converted aircraft radials in both gasoline and diesel form, twin GM 6-71 diesels, and a giant 1100 CID Ford V8. But easily the most unusual engine of the bunch was the 30-cylinder A57 Multibank engine developed in 1941. Essentially, five Chrysler inline sixes were lashed together in a star pattern to form a sort of quasi-radial.

In a nutshell, these schematic views show how the A57 was laid out: five standard Chrysler passenger car engines were configured in a circular pattern, forming one dense and heavy unit. Five helical gears at the ends of the crankshafts drove a sixth gear and an output shaft.

This view of the Multibank engine on its assembly fixture clearly illustrates the clever setup devised by Chrysler lead engineer Harry Woolson and famed Chrysler engine wizard Mel Carpentier. Each of the five L-head inline sixes featured a bore of 3.4375 inches and a stroke of 4.5 inches, displacing 250.6 cubic inches. Total displacement was 1253 cubic inches (21 liters) and the total weight with accessories was nearly 5,250 lbs. Various output figures have been quoted, from 370 hp to 445 hp at 2,400 rpm, and with a very ordinary 6.2:1 compression ratio the engine could run on regular gasoline.

This rear view of a Multibank engine shows the enormous shaft-driven, cast-aluminum cooling fan along with the housing and radiator. Several carburetor and intake systems were tried in an effort to improve fuel distribution. The beautifully restored example shown here was on display at the Walter P. Chrysler Museum for many years, giving many visitors their only opportunity to see the unusual engine. Unfortunately, the museum is now permanently closed.
Between July 1942 and November 1943, some 7,499 Sherman M4 tanks with A57 Multibank engines were built by Chrysler at the Detroit Tank Arsenal in Warren, Michigan. Known as the M4A4, the A57-equipped Sherman (below) required a lengthened hull to accommodate the 30-cylinder engine, which was mounted at the rear with the fan facing aft. (Around 100 M3A4 Lee tanks, the Sheman’s predecessor, were also equipped with the A57.) Most of the M4A4 tanks produced were supplied to the British military under Lend-Lease, and dozens, maybe more, still exist in museums and collections around the world.