Pontiac Straight-8 engine

Pontiac straight-8 engine
Overview
Manufacturer	General Motors
Also called	Silver Streak
Production	1933–1954
Chronology
Predecessor	251 cu in (4.1 L) flathead I/8
Successor	287 cu in (4.7 L) OHV V8

A straight-8 in a 1950 Pontiac Streamliner - note the large intake silencer leading to an oil-bath air cleaner on the far side of the engine

The straight-8 was an eight-cylinder, in-line automobile engine that was used in production Pontiacs from 1933 to 1954. Introduced in the fall of 1932 for the 1933 models, it was Pontiac's most powerful engine at the time and was the least expensive eight-cylinder engine built by an American automotive manufacturer. During its 21-year run, displacement of the "eight" increased twice as platforms grew. It was superseded by Pontiac's new V8, the 287, in 1955.

History

The straight-8 was dubbed the Silver-Streak^[1] at Pontiac Division. Powered by the "eight", a Pontiac was promoted as a likable automobile, with enough power under the hood to get the job done in affordable luxury.

However, by the early 1950s, overhead valve V8s from sister divisions Cadillac, Buick and Oldsmobile, as well as new overhead valve V8s from Ford Motor Company and Chrysler Corporation, made the "Silver Streak" all but obsolete in power, It was a quiet, smooth running engine that served the needs of the 1930s and '40s American consumer adequately for power, if not reliability or economy, but by 1954, the engine was decidedly eclipsed not only by competing auto makers, but by General Motors' own divisions' products as well. Further hamstringing the "Silver Streak" was the aged, but cheap to produce, flathead configuration. Interesting to note that the Strato Streak V-8 was ready to go in 1953, but was held back by the protesting Buick and Olds divisions. Evidence of this is in the details of the chassis/steering of 1953 and 1954 Pontiac's which were designed for the V-8. The V8 configuration of the "Strato-Streak" 287-cubic-inch engine that replaced it in 1955 did away with all the crankshaft and L-head related problems, replacing the Depression era "cheap 8" with a truly modern, durable but yet affordable design perfectly matched to Pontiac's target market. A few years later (fall of 1956), under the guidance of Bunkie Knudsen Pontiac was determined to change its image into a performance car to boost sales, this led Knudsen to look for further talent such as in Pete Estes as chief engineer (taken from Olds division) and John DeLorean as director of advanced engineering,a former Packard and Chrysler engineer. Pontiac became known as a performance division based upon the durable, well performing V8s that came later, all of them based upon the original 287 of 1955.

Market

Designed and priced for conservative lower middle class buyers, the Pontiacs filled a slot between the popular Chevrolet and the higher priced Oldsmobiles and Buicks.

Design

The "eight" was a typical American built engine for its time, a side-valve L-head, or "flathead", with a chain-driven cam. It was naturally aspirated through a Carter "W" series, single or dual-venturi carburetor in downdraft configuration.

Advantages

Of all cylinder layouts without balance shaft a straight eight design has very low inherent vibration, while the side-valve layout contains the moving parts of the valve train within the cast-iron block, enabling it to be very quiet compared to an overhead valve configuration (as in the contemporary Buick engines). Combined with a substantial exhaust manifold and effective intake and exhaust muffling this can lead to a very quiet vehicle, both internally and externally. At the time of its use a quiet engine was thought to be a mark of quality in an automobile. Bores need be of small diameter to keep the engine length down and so strokes must be long to obtain larger displacements - such undersquare configurations exhibit good low RPM torque and are capable of slow idle speeds, enhancing both drivability and quietness. While Chrysler vehicles had similar engines they were not targeted for the lower middle price range enabled by General Motors' manufacturing expertise and volumes of the time.

Disadvantages

As with other iron block straight configurations the engine is considerably heavier than an equivalent V configuration, requiring more materials for the crank and crankcase and so increasing overall vehicle weight in even greater proportion. The long crankshaft tends to exhibit torsional vibration modes under high power, while side-valve flathead engines inhibit smooth intake and exhaust gas flow, limiting power. None of these disadvantages were disabling until the "horsepower race" initiated in the early 1950s ensured the dominance of the overhead valve V8.

Applications

During its run, the "eight" came in all Pontiacs, which included the Special and Deluxe (1936–40), Torpedo (1940–48) and Streamliner (1942–52), as well as the first six years of the Chieftain (1949–58) and the debut year for the Star Chief (1954–66).

Specifications

Compression on the "eight" started at 5.7 - 1 initially,^[2] and was increased to 6.2 - 1 ratio in 1934.^[3] In 1940 it was increased again to 6.5 - 1. From 1952 to 1954 two compression ratios were specified, 6.8-1 with syncromesh (manual) transmission, and 7.7-1 ratio with Hydra-Matic (automatic) transmission.^[4] The engine had a remarkably low idle speed of a 450 rpm with standard transmission and 375 rpm (while in drive) for the automatic;^[5] a modern engine is usually tuned to a minimum 600-700 rpm. The electrical system was a 6-volt primary with a negative ground, and a conventional mechanical ignition, with the firing-order 1-6-2-5-8-3-7-4. The Pontiac engines employed a full pressure oiling system, unlike its Chevrolet cousin.

Below are specifications as per the model year and displacement, with output shown as horsepower (kilowatts).

1933–1935 - 223

1936 - 232

1937–1949 - 249

1950–1954 - 268

"Special"-8

At the General Motors Motorama for 1954, Pontiac debuted its all new Bonneville Special, a concept car envisioned by head designer Harley J. Earl. The concept was equipped with the "Special"-8, a high output 268-cubic-inch (4.39 L) engine that was painted bright red and detailed in chrome. This was a unique configuration for the "eight", installed in the only two Specials ever made. Similar in appearance only, this was a high compression variant that was modified with a high-lift cam and aspirated naturally through four Carter YH side-draft, single barrel carburetors, the same used in the 1953 Corvette, under open-mesh breathers. Total output was the highest ever for the "eight", rated at 230 bhp (170 kW), though some^[14] estimated it at over 300 bhp (220 kW). This estimate may be forgiven as "pride of ownership", but unfortunately it's not credible that these simple modifications would more than double the output of this fairly primitive design, and equal the power per cubic inch of highly developed and purpose-built contemporary sidevalve race engines such as the Harley-Davidson KR. Like the Special, only two of these remarkable variants were ever made.

Note: Pontiac’s new V8 was being considered for use in the Special but was instead held back by GM marketing. They directed that the straight-8 be used, to keep the V8 a secret from consumers for one more year until its debut the following year.^[15]

Footnotes

See also

• Pontiac Straight-6 engine
• Pontiac V8 engine
• List of GM engines