Pontiac straight-6 engine

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.

Pontiac straight-6 engine
Overview
ManufacturerPontiac Division of General Motors
Production1926-1969
Layout
ConfigurationNaturally aspirated Straight-6
Displacement
  • 186.7 cu in (3.1 L)
  • 200 cu in (3.3 L)
  • 208 cu in (3.4 L)
  • 215 cu in (3.5 L)
  • 223 cu in (3.7 L)
  • 230 cu in (3.8 L)
  • 239 cu in (3.9 L)
  • 250 cu in (4.1 L)
Cylinder bore3.25 in (82.6 mm) (186 cuin.)
Piston stroke3.75 in (95.3 mm) (186 cuin.)
Block materialCast iron
Head materialCast iron
ValvetrainSidevalve, OHV or SOHC 2 valves x cyl.
Compression ratio4.8:1, 4.9:1, 6.2:1, 6.5:1, 6.8:1, 7.0:1, 7.7:1
Combustion
Fuel systemRochester Quadrajet or Carter Carburetors
Fuel typeGasoline
Oil systemWet sump
Cooling systemWater-cooled
Output
Power output40–230 hp (29.8–171.5 kW)
Torque output150–193 lb⋅ft (203–262 N⋅m)

"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 T-10 and T-11 (their two lightest trucks) 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.

This engine displaced 186.7 cu in (3.1 L) with a bore and stroke of 3.25 in × 3.75 in (82.6 mm × 95.3 mm) and was rated at 40 hp (30 kW; 41 PS) at 2400 rpm when it was introduced. The compression ratio was 4.8:1.[2]

200

In 1929, the "split head" Pontiac six was increased in displacement to 200 cu in (3.3 L). The horsepower rating increased to 60 hp (45 kW; 61 PS) @ 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.

Flathead Six

208

In 1935, Pontiac re-introduced their six-cylinder engine, as a 208 cu in (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.

223 Pontiac/GMC

The 223 was a side-valve engine, and used a timing chain. The 223 cu in (3.7 L) straight-6 was used in Pontiac automobiles (1937–40) and GMC trucks (1938 only).

239

The 239 cu in (3.9 L) straight-6 was similar in design to previous sixes. It was used from 1941 through 1954 only in Pontiac automobiles.

Specifications
YearModel name (number)DisplacementOutputTorqueCompression Carburetor series (bbl)
1935Master & DeLuxe 6 (6-35)208 cu in (3.4 L)80 hp (59.7 kW)
@ 3600 rpm		150 lb⋅ft (203 N⋅m)
@ 1600 rpm		6.2:1Carter W-1 (1)[3]
1936Master & DeLuxe 6 (6-36)[3]
1937Six (6-37)222.7 cu in (3.6 L)85 hp (63.4 kW)
@ 3520 rpm		161 lb⋅ft (218 N⋅m)
@ 1600 rpm		[3]
1938Six (6-38)[3]
1939Quality & DeLuxe 6 (39-25) & (39-26)Carter WA-1 (1)[3]
1940Special & DeLuxe 6 (40-25) & (40-26)87 hp (64.9 kW)
@ 3520 rpm		164 lb⋅ft (222 N⋅m)
@ 1400 rpm		6.5:1[3]
1941Custom, DeLuxe & Streamliner Torpedo 6 (41-24), (41-25), & (41-26)239.2 cu in (3.9 L)90 hp (67.1 kW)
@ 3200 rpm		175 lb⋅ft (237 N⋅m)
@ 1400 rpm		[3]
1942Torpedo & Streamliner Torpedo 6 (42-25) & (42-26)[3]
1946Torpedo & Streamliner 6 (46-25) & (46-26)93 hp (69.4 kW)
@ 3400 rpm		[3]
1947Torpedo & Streamliner 6 (47-25) & (47-26)[3]
1948Torpedo & Streamliner 6 (48-25) & (48-26)178 lb⋅ft (241 N⋅m)
@ 1400 rpm		[3]
1949Silver Streak 6 (49-25)[3]
1950Silver Streak 6 (50-25)90 hp (67.1 kW)
@ 3400 rpm		178 lb⋅ft (241 N⋅m)
@ 1200 rpm		[3]
1951Silver Streak 6 (51-25)96 hp (71.6 kW)
@ 3400 rpm		191 lb⋅ft (259 N⋅m)
@ 1200 rpm		[3]
1952Silver Streak 6 (52-25) with manual trans.100 hp (74.6 kW)
@ 3400 rpm		189 lb⋅ft (256 N⋅m)
@ 1400 rpm		6.8:1[3]
1952Silver Streak 6 (52-25) with automatic trans.102 hp (76.1 kW)
@ 3400 rpm		7.7:1[3]
1953Chieftain 6 (53-25) with manual trans.115 hp (85.8 kW)
@ 3800 rpm		193 lb⋅ft (262 N⋅m)
@ 2000 rpm		7.0:1Carter WCD (2)[3]
1953Chieftain 6 (53-25) with automatic trans.118 hp (88.0 kW)
@ 3800 rpm		7.7:1[3]
1954Chieftain 6 (54-25) with manual trans.115 hp (85.8 kW)
@ 3800 rpm		7.0:1[4]
1954Chieftain 6 (54-25) with automatic trans.118 hp (88.0 kW)
@ 3800 rpm		7.7:1[4]

Overhead Valve
The 215 cid overhead valve engine in a 1965 LeMans

215

A 215 cu in (3.5 L) 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 215 cu in (3.5 L) aluminum V8 that Pontiac had used in the two years prior, the "Pontiac 215" was an adaptation of Chevrolet's 230 cu in (3.8 L) overhead valve Generation 3 straight-6. Quite different from Pontiac's previous straight-6s, it had a smaller bore 3.75 in (95.3 mm) than the 15 cu in (250 cc) larger Chevrolet engine and a Chevy bellhousing, but its flywheel/flexplate bolt pattern was Pontiac's.

Overhead cam

230
OHC 230 cu in (3.8 L) inline-6

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 230 cu in (3.8 L) 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 165 hp (123 kW).[5] A W53 version for the Firebird produced 215 hp (160 kW).

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.[6]

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 207 hp (154 kW).[5] Power was increased to 215 hp (160 kW; 218 PS) 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.

250
OHC 250 cu in (4.1 L) 1-bbl inline-6 (1968)

The OHC 230 cu in (3.8 L) was enlarged to 250 cu in (4.1 L) for 1968 to 1969. The base engine produced 175 hp (130 kW; 177 PS) while the Sprint versions were rated up to 215 hp (160 kW; 218 PS) with automatic transmissions. The versions with a manual transmission received a hotter camshaft that boosted ratings to 230 hp (172 kW; 233 PS).

See also

References
  1. Stromberg, Austin W., ed. (January 1928). "New GMC Six Has Pontiac Engine". Power Wagon. XL (277): 64.
  2. http://www.Concept%5B%5D Carz.com/vehicle
  3. Motor's Auto Repair Manual, Sixteenth Edition, Motor ,1953
  4. Motor's Auto Repair Manual, Motor,1963
  5. Gunnell, John; Kowalke, Ron (1995). Standard Catalog of Pontiac, 1926-1995. Iola, WI: Krause Publications, Inc. pp. 92–93. ISBN 0-87341-369-5.
  6. "Kaiser Jeep". Ward's Automotive Yearbook. 26: 137. Retrieved 23 March 2016.
  • Pontiac Overhead Cam SIX Forum
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