Is there any piston engine that could possibly inspire as much awe as the ICBM-haulin' GMC Twin Six? What if we said we'd found a 5-bank, 30-cylinder Chrysler for you? Yes, five banks!
Now, we admit that this engine was never intended for use in a car, but tanks are certainly related to cars and so we say this engine qualifies for the Engine Of The Day series. The deal with the A57 was that Chrysler needed to whomp up a tank engine in a hurry, so as to put the kibosh on the Thousand Year Reich and the Greater East Asia Co-Prosperity Sphere. The easiest way to do this was to grab as many existing components off the shelf as possible, so Chrysler used the 201-cubic-inch Plymouth flathead six as the basis for the new engine. Five crankshafts driving a common center shaft via individual ring gears arrayed around a central gear, five heads, five carburetors, five distributors… and 30 cylinders! It was heavy as hell, but it got the job done and was used to power M3A4 Lee and M4A4 Sherman tanks. Here's a video that gives you an idea of this engine's sound: