The Pontiac straight-6 engine is a family of inline-six cylinder automobile engines produced by the Pontiac Division of General Motors Corporation in numerous versions beginning in 1926. "Split Head" Six 186 In the 1920s Oakland Motor Car engineers designed an all new engine for their "companion" make, the Pontiac, that was introduced in 1926. It was a side-valve design with a one piece cast iron block with three main bearings. An unusual feature was that it had two separate cylinder heads that each covered three cylinders. The ignition distributor was mounted on top of the block in the gap between the heads. This engine was also used in GMC's 1927 T-10 and 1928 T-11 (their lightest trucks) as well as their next lightest truck, the T-19, beginning in 1928. Development of the engine shared characteristics with the Oldsmobile Straight-6 engine, as GM worked together to develop the engine for Pontiac combined with the resources of GM-Northway Motor and Manufacturing Division. This engine displaced with a bore and stroke of and was rated at at 2400 rpm when it was introduced. The compression ratio was 4.8:1. 200 In 1929, the "split head" Pontiac six was increased in displacement to . The horsepower rating increased to @ 3000 rpm. Compression was increased slightly to 4.9:1. The "split-head" six was discontinued by Pontiac at the end of the 1932 model year. Pontiac offered only eight-cylinder engines during 1933 and 1934. GMC also switched to the 200 cubic inch engine in 1929, using it into early in the 1933 model year. Flathead Six 208 In 1935, Pontiac re-introduced their six-cylinder engine, as a straight-6. The 208 was produced in 1935 and 1936. It was a side-valve design with a timing chain, as was popular at the time. This engine featured a conventional one piece cylinder head, and the distributor was moved to the side of the block. The number of main bearings was increased to four. Like the Pontiac Straight-8 engine it also featured full-pressure oiling and insert type precision main and rod bearings. These two latter features greatly increased longevity and durability especially under high speed conditions. 223 Pontiac/GMC The 223 was a side-valve engine, and used a timing chain. The straight-6 was used in Pontiac automobiles (1937–40) and GMC trucks (1938 only). 239 The straight-6 was similar in design to previous sixes. It was used from 1941 through 1954 only in Pontiac