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

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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.

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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.

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|1936||Master & DeLuxe 6 (6-36)||

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|1954||Chieftain 6 (54-25) with automatic trans.||<br/>@ 3800 rpm||7.7:1|| It was offered with a single one barrel carburetor, rated at . A W53 Sprint version for the Firebird produced up to .

Considered advanced by Detroit engineering standards at the time, the Pontiac OHC 6 followed the Jeep Tornado I6 as the second post-World War II domestic-developed and mass-produced overhead cam automobile engine.

The Pontiac's single camshaft was supported by journals within the aluminum valve cover; no separate bearing shells were used. The cam was driven by a noise-reducing fiberglass-reinforced cogged rubber belt instead of the usual metal chain or gears. Valves were opened with finger followers (centered under the cam) that pivoted at one end on stationary hydraulic adjusters. The oil pump, distributor, and fuel pump were driven by an external jackshaft powered by a rubber timing belt nestled within an aluminum housing bolted to the right side of the block. The head had a single port face with both exhaust and intake valves on the left side and valve stems strongly tilted towards the left. This engine was used in the 1966-67 Tempest and Le Mans and 1967 Firebird.

An optional high-performance Sprint version featured high-compression pistons, hotter cam, dual valve springs, split/dual exhaust manifold, stronger coil, and the then new Rochester Quadrajet carburetor. rated at . Power was increased to in 1967.

Like other Pontiac engines of the era, the OHC 6 was not available in Canada with the exception of the Sprint version of the Firebird. Canadian-market Pontiac automobiles were equipped with the Chevrolet OHV six.

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thumb|right|OHC 1-bbl inline-6 (1968)

The OHC was enlarged to for 1968 to 1969. The base engine produced while the 4 bbl Quadrajet Sprint versions were rated up to with automatic transmissions. The versions with a manual transmission received a hotter camshaft that boosted ratings to .

See also

  • Pontiac Trophy 4 engine
  • Pontiac straight-8 engine
  • Pontiac V8 engine
  • List of GM engines

References

  • [https://web.archive.org/web/20090705121503/http://sohcsix.yuku.com/bsohcsix] Pontiac Overhead Cam SIX Forum