The Chrysler flathead engine is a flathead automotive engine manufactured by the Chrysler Corporation from 1924 through the early 1960s. The flathead engine came in four-,six-, and eight-cylinder configurations and varying displacement, with both a cast iron and cast aluminum cylinder head. It was installed in Chrysler, DeSoto, Dodge and Plymouth branded vehicles.

Chrysler introduced a straight-four in 1926 when the Maxwell Motor Corporation was re-organised into the Chrysler Corporation in 1925.^[1] Initially used by Chrysler, the straight-four was fitted to Plymouth cars and Dodge light trucks beginning in 1929, lasting in production through 1933.

The original version displaced 185.8 cu in (3,044 cc) and produced 38 hp (28 kW). This was only produced in 1926, with displacement reduced to 170.3 cu in (2,791 cc) for 1927 and 1928. Power was initially rated the same but was upped to 45 hp (34 kW) during the 1928 model year.

After the introduction of the Plymouth brand in 1929, the base engine has been subjected to a major redesign and enlarged to 175.4 cu in (2,874.3 cc) with the power rating remaining the same. It also equipped Dodge light trucks in 1929–1930. It was enlarged again to 196.1 cu in (3,213 cc) in 1930 with 48 hp (36 kW). The engine was revised for 1931 with 56 hp (42 kW) and 1932 with 65 hp (48 kW) for Plymouth only, Dodge continued with the 48 hp (36 kW) from 1931 to 1933. A small-bore version was developed for export markets in 1931, with a narrower bore which brought the RAC rating down from 21 to 15.6 hp. For 1932 the bore was reduced further, bringing the tax horsepower rating to just beneath 15.5.

Chrysler did not offer a four-cylinder engine again until 1981 with the Chrysler 2.2 & 2.5 engine used in the Chrysler K platform.

The first six-cylinders was the B-Model (seven main bearings) and introduced in 1924 with the first Chrysler Corporation production, the B70.^[1] An upscale version designated E-Model equipped the new Chrysler Imperial E80 in 1926, and a downscale one named H-Model followed in 1927 (Chrysler Series 70). After the purchase of Dodge Brothers Inc. in 1928, Chrysler Corporation had five straight-6s in production with the addition of the Victory and Senior Dodge Brothers engines.^[1]

So, with the introduction of the new Desoto brand in 1929, came a new and cheaper to product six cylinders, the K-Model (four main bearings, deep skirts).^[1] By mid-1930, it partially replaced the previous engines in varying displacements on passenger cars, in conjunction with an all-new straight-8 block. Only the Imperial's engine remains in production for the Dodge Trucks^[1] 2-ton Models F-40 & K-50, 3-ton models F-60 & K-70, 2 & 3-ton Special, buses from 1930 to 1934-35. To replace these two engines, a new and very large six cylinders was launched in late 1936 (331 cu. in.). The 1956 C-3 Series was the last to use this big straight-6 (413 cu. in.).

In 1932, the Ford's V8 flathead launch shook up the market. The demand for larger engines was even for entry-level brands. A new straight-6 for Plymouth (PC/PD) and Dodge (DP/DQ) came in production in 1933 (shallow skirt, known as the "23 in block", with a head desk length of 580 mm), followed by a larger variant for Desoto (S3) and Chrysler Royal C16) in 1937 ("25 in block" – 640 mm), marking the K-Model end. There is one exception to this: when Chrysler established an engine foundry in Windsor, Canada in 1938, it was decided to only use the long block for all Canadian-built engines. These engines received a trailing "C" in their designation, becoming P8C for example. Thanks to judicious dimensioning, the Canadian 201- and 218-cubic inch engines had nearly identical displacement to their American cousins.^[3]

Beginning in 1938, the 201 cu in (3,299 cc) inline-six was used in Massey Harris's Model 101 tractor (later known as the 101 Super). It continued to be used by Massey until 1940, when it was supplanted by the 218 cu in (3,568 cc).^[4] In 1940, Chrysler's 242 cu in (3,966 cc) straight six went into Massey's 201 Super, which lasted until 1942.^[4]

During World War II, the 251 cu in (4,107 cc) flathead six was used as the basis for the Chrysler A57 multibank tank engine.^[5]

The last automotive use of the Chrysler flathead inline-six was in 1968. It was replaced by the much more efficient OHV Slant-6 released in 1960, which appeared in most Dodge trucks starting in 1961. According to the Standard Catalog of American Light-Duty Trucks, the Dodge Power Wagon WM300 used the 251 inline flathead six until 1968, after which the Dodge WM300 was dropped for the 1969 production year. The flathead remained in production until the early 1970s for industrial and agricultural use.^{[citation needed]}

The new in-line 8-cylinder engine is largely based on the six-cylinder engine that appeared on the Desoto Model K. It has five main levels, the central one being wider.^[1] When the engineers had to rebore the cylinders to 3-1/2 inches, the space between each pair of cylinders was modified. This applies to all blocks with the same bore.

In the case of the Imperial (CG, CH) then Custom imperial (CL, CW), a new and unique straight-8 engine was created with 9 main bearings and equipped with a two-barrel downdraft carburetor. From the CW model, the cylinder head is made of aluminium. It also powered the Dodge Trucks G-80 models (1931-1934) and Fargo buses (1930-1932).^[1]

Wikimedia Commons has media related to Chrysler flathead engine.

• List of Chrysler engines