The Chrysler Flathead engine is an automotive engine manufactured by the Chrysler Corporation.
Chrysler introduced a straight-4

Straight-4

The inline-four engine or straight-four engine is an internal combustion engine with all four cylinders mounted in a straight line, or plane along the crankcase. The single bank of cylinders may be oriented in either a vertical or an inclined plane with all the pistons driving a common crankshaft....

 derivative of their new Flathead straight-6

Straight-6

The straight-six engine or inline-six engine is a six-cylinder internal combustion engine with all six cylinders mounted in a straight line along the crankcase...

 in 1926. Initially used by all Chrysler divisions, the straight-4 became Plymouth

Plymouth (automobile)

Plymouth was a marque of automobile based in the United States, produced by the Chrysler Corporation and its successor DaimlerChrysler.-Origins:...

-only in 1929, lasting in production through 1932.

The original version displaced 185.8 cubic inch and produced 38 hp (28 kW).