Like most American automobile manufacturers, Pontiac relied on the straight-6 design for their circa-World War II automobiles.
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In the 1920s Oakland Motor Car engineers designed an all new engine for their "companion" make, the Pontiac, which 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 displaced 186.7 cubic inches (3,059 cc) (3.25x3.75) and was rated at 40 bhp (29.4 kW) @ 2400 rpm when it was introduced. The compression ratio was 4.8-1.[1]
In 1929, the "split head" Pontiac six was increased in displacement to 200.0 cubic inches (3,277 cc). The horsepower rating increased to 60 bhp (44.2 kW) @ 3000 rpm. Compression was increased slightly to 4.9-1.[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.
In 1935, Pontiac re-introduced their six cylinder engine, as a 208-cubic-inch (3.4 L) 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.
Just as was done with their later V8s, Pontiac shared their mainstream straight-6 engine with GMC for truck use. It was also a side-valve engine, and used a timing chain. The 223-cubic-inch (3.7 L) straight-6 was used in Pontiac automobiles (1937–40) and GMC trucks (1938 only).
The 239-cubic-inch (3.9 L) 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 cu in |
Output BHP (kW) @ RPM | Torque ft·lbf. (Nm) @ RPM | Compression | Carburetor series (bbl) | |
1935 | Master&DeLuxe 6 (6-35) | 208.0 | 80 (58.88) @3600 | 150(203.40) @ 1600 | 6.2-1 | Carter W-1 (1) | [2] |
1936 | Master&DeLuxe 6 (6-36) | 208.0 | 80 (58.88 @ 3600 | 150 (203.40) @ 1600 | 6.2-1 | Carter W-1 (1) | [2] |
1937 | Six (6-37) | 222.7 | 85 (62.56) @ 3520 | 161 (218.32) @ 1600 | 6.2-1 | Carter W-1 (1) | [2] |
1938 | Six (6-38) | 222.7 | 85 (62.56) @ 3520 | 161 (218.32) @ 1600 | 6.2-1 | Carter W-1 (1) | [2] |
1939 | Quality&DeLuxe 6 (39-25) & (39-26) | 222.7 | 85 (62.56) @ 3520 | 161 (218.32) @ 1600 | 6.2-1 | Carter WA-1 (1) | [2] |
1940 | Special&DeLuxe 6 (40-25) & (40-26) | 222.7 | 87 (64.03) @ 3520 | 164 (222.38) @ 1400 | 6.5-1 | Carter WA-1 (1) | [2] |
1941 | Custom,DeLuxe & Streamliner Torpedo 6 (41-24),(41-25),& (41-26) | 239.2 | 90 (73.59) @ 3200 | 175(237.30) @ 1400 | 6.5-1 | Carter WA-1 (1) | [2] |
1942 | Torpedo & Streamliner Torpedo 6 (42-25) & (42-26) | 239.2 | 90 (73.59) @ 3200 | 175 (237.30) @ 1400 | 6.5-1 | Carter WA-1 (1) | [2] |
1946 | Torpedo & Streamliner 6 (46-25) & (46-26) | 239.2 | 93 (68.45) @ 3400 | 175 (237.30) @ 1400 | 6.5-1 | Carter WA-1 (1) | [2] |
1947 | Torpedo & Streamliner 6 (47-25) & (47-26) | 239.2 | 93 (68.45) @ 3400 | 175 (237.30) @ 1400 | 6.5-1 | Carter WA-1 (1) | [2] |
1948 | Torpedo & Streamliner 6 (48-25) & (48-26) | 239.2 | 93 (68.45) @ 3400 | 178 (241.37) @ 1400 | 6.5-1 | Carter WA-1 (1) | [2] |
1949 | Silver Streak 6 (49-25) | 239.2 | 93 (68.45) @ 3400 | 178 (241.37) @ 1400 | 6.5-1 | Carter WA-1 (1) | [2] |
1950 | Silver Streak 6 (50-25) | 239.2 | 90 (66.24) @ 3400 | 178 (241.37) @ 1200 | 6.5-1 | Carter WA-1 (1) | [2] |
1951 | Silver Streak 6 (51-25) | 239.2 | 96 (70.65) @ 3400 | 191 (259.00) @ 1200 | 6.5-1 | Carter WA-1 (1) | [2] |
1952 | Silver Streak 6 (52-25) with manual trans. | 239.2 | 100(73.59)@3400 | 189(256.28)@1400 | 6.8-1 | Carter WA-1 (1) | [2] |
1952 | Silver Streak 6 (52-25) with automatic trans. | 239.2 | 102(75.07)@3400 | 189 (256.28)@1400 | 7.7-1 | Carter WA-1 (1) | [2] |
1953 | Chieftain 6 (53-25) with manual trans. | 239.2 | 115(84.63)@3800 | 193(261.71)@2000 | 7.0-1 | Carter WCD (2) | [2] |
1953 | Chieftain 6 (53-25) with automatic trans. | 239.2 | 118 (86.84@3800 | 193(261.71)@2000 | 7.7-1 | Carter WCD (2) | [2] |
1954 | Chieftain 6 (54-25) with manual trans. | 239.2 | 115(84.63@3800 | 193(261.71)@2000 | 7.0-1 | Carter WCD(2) | [3] |
1954 | Chieftain 6 (54-25) with automatic trans. | 239.2 | 118(86.84)@3800 | 193(261.71)@2000 | 7.7-1 | Carter WCD(2) | [3] |
In the mid-1960s, Pontiac revived their straight-6 for a short time. Although it was of a different displacement, this Pontiac engine was based on Chevrolet's Generation 3 straight-6.
The 215-cubic-inch (3.5 L) straight-6 was produced in 1964 and 1965. It is sometimes confused with the 215 aluminum V8 used in the two years prior. It was an OHV/pushrod engine design, quite different from the previous Pontiac straight-6 engines. It was a smaller bore (3.75") version of the 230 cubic inch Chevrolet inline 6.
The OHC-6 design was adopted by Pontiac in the 1966 model year. The block was based on the Chevrolet Straight-6, but had block and head castings unique to the OHC. Both head and block were cast iron; only the large cam carrier/valve cover was aluminum. The engine featured a Single Over Head Cam and was the base engine in the Pontiac Tempest.
The Pontiac OHC-6 engine shared internal dimensions with the standard 230-cubic-inch (3.8 L) Chevrolet I6 block. The OHC head design put it in the avante garde of Detroit engineering. The single camshaft was supported by journals within the aluminum valve cover; no separate bearing shells were used. The cam was driven by a glass fiber-reinforced cogged rubber belt, instead of the usual metal chain or gears, making it state of the art for the time, as well as very quiet. Valves were opened with finger followers (centered under the cam) that pivoted at one end on stationary hydraulic adjusters. The oil pump, distributor drive and fuel pump drive were not within the block, but were handled by an external jackshaft in an aluminum housing that bolted to the right side of the block. The jackshaft was driven by the rubber timing belt. The head had a single port face (exhaust and intake were both on the left side) and the valve stems were strongly tilted towards the left. This engine was used on the 1966 through 1969 Tempest and Le Mans and the 1967 through 1969 Firebird.
A high-performance version, called the Sprint, was an option. The Sprint featured high-compression pistons, a hotter cam, dual valve springs, a split/dual exhaust manifold, a better coil and utilized the then new Quadrajet 4-barrel carburetor. It was the first American high performance in-line six cylinder engine since the 1954 Chevrolet Corvette.
The Pontiac OHC-6 engine ended production with the 1969 models.
Like other Pontiac engines of the era, it was not available in Canada; Canadian Pontiac automobiles came with the Chevrolet OHV six instead.
The 230 OHC-6 engine was produced in 1966 and 1967. Power output was rated at 165 bhp (123 kW) from a displacement of 230-cubic-inch (3.8 L). The high performance Sprint version produced 207 bhp (154 kW).
The 250ci Engine (4.1L) replaced the 230ci (3.8L) from 1968 to 1969. The base engine produced 175 hp while the Sprint versions were rated up to 215 hp with an automatic transmission. The versions with a manual transmission received a hotter camshaft which boosted the horsepower ratings to 230 hp.