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Big block, small block, Y-block, B-block, etc…

A few years back, my colleague Mathieu St-Pierre wrote a piece for entitled “Small Block and Big Block V8? What’s the Difference? In it, he tried to answer a question that has long bedeviled fans of American V8s: just what is the difference between big block and small block engines?

Mathieu, unfortunately, had to admit in his article to not having unearthed the precise answer, although he did mention that the term was first used when General Motors launched its “small” 265-cubic-inch V8 in its 1955 Chevrolet. He was correct in asserting this, but did not elaborate further. Here, now, is the explanation.

In the years after the end of World War II, American automakers (who in that era made up the biggest car-making sector in the world) wanted to rejuvenate their vehicle lineups, including their mechanics. Several models switched from 8-cylinder in-line engines or side-valve (or flathead) V8s, which were so popular before the war, to new overhead-valve V8 engines that were more compact and especially more powerful.

Their design nonetheless still required a thick and heavy construction. One of the engines produced was the V8 offered with the 1949 Cadillac and Oldsmobile models. Powerful and especially quick, this engine type began to become widespread in car racing (for example in the Oldsmobiles racing in NASCAR, and the Cadillacs running in the 24 Hours of Le Mans). The engineering for this engine had been developed by Ed Kelley, who was asked to do the same for Chevrolet.

Kelley, however, proved unable to produce one for the company. In the early 1950s, GM’s brain trust brought on board an engineer by the name of Ed Cole, who was posted to the company’s tank and armoured vehicle division. Where Kelley had been unable to detach himself from the principle of a massive cylinder block, Cole came up with a lighter technique for casting metal, which would require greater precision when grinding. This new technique became known as thin wall casting, and it allowed for the development of smaller V8 engines. From this originated the term “small block”, in contrast with the older, larger engines, henceforth known as “big block” engines. Cole, by the way, had managed to decrease the thickness of the metal casting from 22 to 9 sand molds.
The first small-block V8 from Chevrolet to see the light of day was the 1955 model, with a displacement of 265 cubic inches. Subsequent models saw this increase to 283, 307, 327, 350 and 400, with the company also producing various 265, 302 and other short-term editions. Today, GM still produces its small black V8s using the same configuration as that first 1955 model, refined of course with some modern improvements. It should be mentioned that no components of the company’s modern engines fit on its older versions, unless you’re an expert in customization who knows how to make them fit.                         

GM continued to produce big block engines into the 1980s, with the manufacturer’s larger trucks the last to house them under their hoods. Nowadays Chevrolet is able to produce very high-performance 7.0L V8s (with a displacement of 427 cubic inches) based on the small block principle, as opposed to the 427 and 545 big blocks of the 1970s. The company’s Pontiac, Oldsmobile and Buick divisions eventually followed Chevrolet’s lead and created their own versions of the small block engine.

Aside from a need to rejuvenate its Chevrolet vehicles, another of the factors behind GM’s push for development of small block V8s in the early 1950s was a desire to go after the clientele of Ford (whose cars had featured side-valve V8 engines since 1932). By 1954, Ford was getting ready to replace its flathead engines with new Y-block V8s, which featured cylinder blocks that rose vertically at the level of the crankshaft to create a Y-shape. The Y-block (272, 292, 312, 352) was however relatively heavy, and the American number-two automaker set out to develop its own version of the thin-wall motor.

In 1962, the company unveiled the Challenger V8 engine with 221 cubic inches of displacement, which would become the 260, 289, 302, 351 and others; it was Ford’s version of the small block engine. It would become known to many as the Cobra, after the 260 was used by Carroll Shelby in creating the legendary Cobra roadster. This motor does not exist anymore today, other than with Ford Racing (as a special order for hot-rodders or for competitions). It can do up to 7 litres (Roush 427).

At Chrysler (today FCA), the process played out in somewhat similar fashion. The automaker had big HEMI V8s, then B-blocks. But these engines were too heavy for the new compact cars they were coming out with. From the company’s A and LA (Light A) engines were born Chrysler’s small block version, which made its debut as the 273 cubic-inch Commando V8 in 1964. This engine would become a 318, then a 340 and even a 360 before disappearing…

GM was the sole manufacturer to hold on to its original small block engine, albeit in a largely unrecognizable form. The construction process has gone transformational changes over the decades; most manufacturers have opted for an overhead camshaft configuration (GM’s small block and FCA (Chrysler)’s HEMI V8 have retained the conventional camshaft). But despite the extinction of the big blocks (even in trucks), true-blue fans of car mechanics prefer to continue to use the terms small blocks and large blocks. Of course, it’s an open question whether younger car lovers could tell them apart at car shows or in the paddocks at racing events!

(Ref.: Chevrolet 1955, Creating the original, Michael Lamm, Lamm-Morada (Motorbooks International), 1991.)  


Original small block: The small Chevrolet V8 with 265 cubic inches of displacement is at the origin of the term small block.
Photo: GM
Original small block: The small Chevrolet V8 with 265 cubic inches of displacement is at the origin of the term small block.
Big block: A perfect example of the big block engine, this 429 cubic-inch Ford Shot Gun is visibly massive!
Photo: Ford
Big block: A perfect example of the big block engine, this 429 cubic-inch Ford Shot Gun is visibly massive!