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1955-1957 Pontiac Strato-Streak

Pontiac's Engine

Under the hood lurked a brand-new overhead-valve "Strato-Streak" V-8 engine. It wasn't much bigger than its flat-head, straight-eight predecessor -- 287.2 versus 268.4 cubic inches -- but it generated 42 percent more horsepower and 13 percent more torque. Performance figures, as recorded by Motor Trend, speak for themselves:

Top speed, mph 100.3
1/4-mile, seconds 19.7
1/4-mile, mph
0-30 mph, seconds4.4
0-60 mph, seconds13.817.4
30-50 mph, seconds
50-80 mph, seconds

With the 200-bhp "Power Pack," Motor Trend knocked the 0-60 time down to 12.7 seconds, nearly five seconds faster than the 1954 straight-eight!

This isn't to suggest that the old Pontiac Eight wasn't a good engine. Designed in the early 1930s by Ben Anibal, formerly chief engineer at Cadillac, it was a durable, relatively economical unit, one of the most serviceable engines of its day. Good enough, in fact, that in 1937 Oldsmobile abandoned its previous design in favor of an engine that bore, unmistakably, a filial resemblance to the Pontiac Eight.

However, not to put too fine a point on the matter, Pontiac's V-8 was overdue. Oldsmobile had introduced its short-stroke, overhead-valve "Rocket" V-8 in 1949, Studebaker released its short-stroke in 1951, Dodge and Buick in 1953, Mercury in 1954, leaving Pontiac as the only automaker in its price class to retain the old-fashioned, under-square, L-head, eight-in-line engine.

As a matter of fact, research on V-8 engines had begun at Pontiac as early as 1946, although at that time there was no real urgency about its development. The old flathead, in its fourteenth year of production by that time, was still popular -- and still giving a good account of itself.

In time, competitive pressures would force Pontiac's management to reassess its position, but in 1946 -- with postwar demand for new cars far exceeding the available supply -- the ultra-conservative Harry Klinger, Pontiac's general manager since 1933, had every reason to feel complacent.
In the initial stages of the V-8's development, Pontiac's engineers experimented with the division's traditional L-head layout. No doubt this had something to do with their familiarity with this type of design. But it's safe to say that cost considerations were also taken into account, for due to its simplicity, a side-valve engine was significantly cheaper to manufacture than the overhead-valve type.

In time, however, it became evident to Ed Delaney, Pontiac's chief engineer -- as it had, earlier, to Cadillac engineers -- that the L-head design was simply not compatible with the higher compression ratios that the future was expected to bring. So in the end, Pontiac -- like the Cadillac, Oldsmobile, and Buick Divisions before it (and Chevrolet almost simultaneously) -- settled on overhead valves. Engineer Mark Frank was put in charge of the new engine's development, assisted by Edmund Windeler and Clay-ton Leach.

Incidentally, the original intent had been for Pontiac to continue offering a six-cylinder car as a companion to the new V-8. Several prototype sixes were built, including a V-6 and an overhead-valve, inline version, and consideration was even given to retaining the aged flathead. But by 1954, sixes made up less than eight percent of Pontiac's total production, so it was only logical that all 1955 models should get the new V-8.

Following the example of its colleagues at the other General Motors divisions, Pontiac adopted an over-square design (larger bore than stroke). Thus, friction was reduced, and larger valves could be employed, leading to improved breathing. A monobloc casting was used, with a 90-degree angle between the cylinder banks, while a central camshaft operated the pushrod and rocker-arm valve gear to each side.

Up to this point the proposed Pontiac design wasn't appreciably different than Oldsmobile's -- or Buick's or Cadillac's, for that matter. What set the Pontiac engine apart was its overhead-valve gear, called the "Ball-Pivot Valve Train." Working at home on his own time, Assistant Engineer Clayton Leach developed a new type of mechanism in which the usual rocker-arm shafts were eliminated. It was thereby considerably simplified, and weight was substantially reduced.

In Leach's design, rocker arms were made of cyanide-hardened stamped steel. Each arm was individually mounted on a ball pivot, which in turn was fitted to a stud protruding from the cylinder head. Misalignment of the rocker arm relative to the pushrod and valve stem was eliminated because the rocker arm was able to square itself on the end of the valve stem. Not only was the mechanism much lighter than the traditional rocker shaft arrangement, it was a whole lot cheaper to manufacture.

Some automotive journalists, notably the well-known Floyd Clymer, expressed doubts about the durability of Clayton Leach's valve gear, and indeed it represented a radical departure from past practices. So George Delaney -- a cautious, conservative man by nature -- subjected it to test after test until he was satisfied that it was fully as serviceable as the older, heavier setup used by the other General Motors divisions.

Pontiac boasted, "On the road and in the laboratory -- pre-proved in over three million test miles!" So satisfactory was the layout, in fact, that it caught the eye of Ed Cole, who had just recently come from Cadillac to become chief engineer at the Chevrolet Division. Cole wanted Leach's valve gear for the new V-8 that he and Harry Barr were developing for the 1955 Chevy.

To read about the new Pontiac's performance in its division, see the next page.

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