Pontiac straight-8 engine
Overview
Manufacturer	Pontiac (General Motors)
Also called	Silver Streak
Production	1933–1954
Layout
Configuration	Naturally aspirated Straight-8 cylinder
Displacement	223 cu in (3.7 L) 233 cu in (3.8 L) 249 cu in (4.1 L) 268 cu in (4.4 L)
Cylinder block material	Cast iron
Cylinder head material	Cast iron
Valvetrain	Flathead
Compression ratio	5.7:1, 6.8:1, 7.7:1
Combustion
Fuel system	Carter Carburetor
Fuel type	Gasoline
Oil system	Full pressure
Cooling system	Water-cooled
Output
Power output	77–127 bhp (57–95 kW)
Torque output	153–234 lb⋅ft (207–317 N⋅m)
Chronology
Predecessor	251 cu in (4.1 L) flathead I8
Successor	287 cu in (4.7 L) OHV V8

The Pontiac straight-8 engine is an inline eight-cylinder automobile engine produced by Pontiac 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 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 It was superseded by Pontiac's new V8, the 287, in 1955. Engine block and cylinder heads were cast at Saginaw Metal Casting Operations then assembled at Tonawanda Engine before delivery to Pontiac Assembly for installation.^[1]

The straight-8 was dubbed the Silver-Streak^[2] at Pontiac Division. Powered by the "eight", optional in lower-end models, 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, powerful overhead valve V8s from sister GM Divisions Cadillac, Buick and Oldsmobile, as well as new overhead valve V8s from Ford Motor Company and Chrysler Corporation, made the flathead "Silver Streak" all but obsolete. It was a quiet, smooth running, cheap to produce engine that served the needs of the 1930s and '40s Pontiac buyers adequately for power. By 1953 the 287-cubic-inch (4.7 L) Strato Streak V8 was ready to go, with Pontiac chassis and steering already adapted for it, but it was held back by the protesting Buick and Olds divisions.^{[citation needed]} It was a truly modern, durable but 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, including 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.

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.

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 (one- or two-barrel) downdraft carburetor.

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 and vibration free 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 configurations (called "undersquare") 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.

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.

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).

Compression on the "eight" started at 5.7:1 initially,^[3] and was increased to 6.2:1 in 1934.^[1] In 1940 it was increased again to 6.5:1. From 1952 to 1954 two compression ratios were specified, 6.8:1 with synchromesh (manual) transmission, and 7.7:1 with Hydramatic automatic transmission.^[4] The engine had a remarkably low idle speed of 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 and full bearing inserts, unlike its Chevrolet cousin.

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

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 (4.4 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, modified with a high-lift cam and fitted with four Carter YH side-draft one-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 (172 kW), though some estimated it at over 300 bhp (224 kW).^[14] Like the Special, only two 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-eight be used to keep the V8 a secret from consumers for one more year until its debut the following year.^[15]

• Pontiac Trophy 4 engine
• Pontiac straight-6 engine
• Pontiac V8 engine
• List of GM engines