| Pontiac straight-6 engine | |
| Manufacturer: | Pontiac (General Motors) |
| Production: | 1926-1969 |
| Configuration: | Naturally aspirated Straight-6 |
| Valvetrain: | Sidevalve OHV or SOHC (1964-1969) |
| Block: | Cast iron |
| Head: | Cast iron |
| Fueltype: | Gasoline |
| Fuelsystem: | Rochester Quadrajet or Carter Carburetors |
| Coolingsystem: | Water-cooled |
| Oilsystem: | Wet sump |
| Bore: | 3.25inches (186 cuin.) |
| Stroke: | 3.75inches (186 cuin.) |
| Compression: | 4.8:1, 4.9:1, 6.2:1, 6.5:1, 6.8:1, 7.0:1, 7.7:1 10.5:1 |
| Power: | NaN1NaN1 |
| Torque: | NaN0NaN0 |
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.
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.[1] 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 186.71NaN1 with a bore and stroke of NaNinches and was rated at 400NaN0 at 2400 rpm when it was introduced. The compression ratio was 4.8:1.[2]
In 1929, the "split head" Pontiac six was increased in displacement to 2001NaN1. The horsepower rating increased to 600NaN0 @ 3000 rpm. Compression was increased slightly to 4.9:1.[2] 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.
In 1935, Pontiac re-introduced their six-cylinder engine, as a 2081NaN1 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.
The 223 was a side-valve engine, and used a timing chain. The 2231NaN1 straight-6 was used in Pontiac automobiles (1937–40) and GMC trucks (1938 only).
The 2391NaN1 straight-6 was similar in design to previous sixes. It was used from 1941 through 1954 only in Pontiac automobiles.
| Year | Model name (number) | Displacement | Output | Torque | Compression | Carburetor series (bbl) | |
| 1935 | Master & DeLuxe 6 (6-35) | 2081NaN1 | 801NaN1 @ 3600 rpm | 1500NaN0 @ 1600 rpm | 6.2:1 | Carter W-1 (1) | [3] |
| 1936 | Master & DeLuxe 6 (6-36) | ||||||
| 1937 | Six (6-37) | 222.71NaN1 | 851NaN1 @ 3520 rpm | 1610NaN0 @ 1600 rpm | |||
| 1938 | Six (6-38) | ||||||
| 1939 | Quality & DeLuxe 6 (39-25) & (39-26) | Carter WA-1 (1) | |||||
| 1940 | Special & DeLuxe 6 (40-25) & (40-26) | 871NaN1 @ 3520 rpm | 1640NaN0 @ 1400 rpm | 6.5:1 | |||
| 1941 | Custom, DeLuxe & Streamliner Torpedo 6 (41-24), (41-25), & (41-26) | 239.21NaN1 | 901NaN1 @ 3200 rpm | 1750NaN0 @ 1400 rpm | |||
| 1942 | Torpedo & Streamliner Torpedo 6 (42-25) & (42-26) | ||||||
| 1946 | Torpedo & Streamliner 6 (46-25) & (46-26) | 931NaN1 @ 3400 rpm | |||||
| 1947 | Torpedo & Streamliner 6 (47-25) & (47-26) | ||||||
| 1948 | Torpedo & Streamliner 6 (48-25) & (48-26) | 1780NaN0 @ 1400 rpm | |||||
| 1949 | Silver Streak 6 (49-25) | ||||||
| 1950 | Silver Streak 6 (50-25) | 901NaN1 @ 3400 rpm | 1780NaN0 @ 1200 rpm | ||||
| 1951 | Silver Streak 6 (51-25) | 961NaN1 @ 3400 rpm | 1910NaN0 @ 1200 rpm | ||||
| 1952 | Silver Streak 6 (52-25) with manual trans. | 1001NaN1 @ 3400 rpm | 1890NaN0 @ 1400 rpm | 6.8:1 | |||
| 1952 | Silver Streak 6 (52-25) with automatic trans. | 1021NaN1 @ 3400 rpm | 7.7:1 | ||||
| 1953 | Chieftain 6 (53-25) with manual trans. | 1151NaN1 @ 3800 rpm | 1930NaN0 @ 2000 rpm | 7.0:1 | Carter WCD (2) | ||
| 1953 | Chieftain 6 (53-25) with automatic trans. | 1181NaN1 @ 3800 rpm | 7.7:1 | ||||
| 1954 | Chieftain 6 (54-25) with manual trans. | 1151NaN1 @ 3800 rpm | 7.0:1 | [4] | |||
| 1954 | Chieftain 6 (54-25) with automatic trans. | 1181NaN1 @ 3800 rpm | 7.7:1 |
A 2151NaN1 overhead valve straight-6 was produced in 1964 and 1965 but was not an original Pontiac design. Sometimes confused with the Buick designed and built 2151NaN1 aluminum V8 that Pontiac had used in the two years prior, the "Pontiac 215" was an adaptation of Chevrolet's 194 cu.in. inline 6 currently produced and the new 2301NaN1 overhead valve Turbo-Thrift straight-6. Quite different from Pontiac's previous straight-6s, it had a smaller bore 3.75inches than the 15cuin larger Chevrolet engine and a Chevy bellhousing, but its flywheel/flexplate bolt pattern was Pontiac's.
A single overhead camshaft (SOHC) design was introduced by Pontiac in the 1966 model year as the standard engine in the Tempest. Offered also in 1967, the 2301NaN1 OHC 6 shared internal dimensions with the overhead valve Chevrolet straight-6 engine it was based on, but had unique cast iron block and head castings. Only the large cam carrier/valve cover was aluminum. It used jackshaft (outside of the block) for oil pump and distributor drive. The jackshaft was driven by the fiberglass reinforced timing belt.[5] It was offered with a single one barrel carburetor, rated at 1650NaN0.[6] A W53 Sprint version for the Firebird produced up to 215hp. 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.[7]
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 2070NaN0.[8] Power was increased to 2150NaN0 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.
The OHC 2301NaN1 was enlarged to 2501NaN1 for 1968 to 1969. The base engine produced 1750NaN0 while the 4 bbl Quadrajet Sprint versions were rated up to 2150NaN0 with automatic transmissions. The versions with a manual transmission received a hotter camshaft that boosted ratings to 2300NaN0.