Small block and big block V8? What's the difference?

Small block and big block V8? What's the difference?
Simple question isn't it? Everyone thinks that it has to do with engine displacement; you know, 396 Ci or 455 or whatever your favourite American car maker says is the most badass number. It turns out that this is not always actually the case. Or is it?

The question came up because GM celebrated its 100-millionth small block recently, a milestone 56 years in the making. Big block V8s were produced in the 50s and 60s and have never made a comeback but we still hear lots about them.

I had a discussion with a muscle-car enthusiast at the office and both of us knew that the answer did not lie solely in cubic inches. Somehow, it had to do with the size or position of the engine block as well.

Ever look up the answer on the internet? I have and it's quite a mess. One thing that everyone seems to agree on is that General Motors was the first manufacturer to coin the “small block” term sometime around 1955. From then on, engine displacements began to take massive proportions as the original horsepower and torque wars flared up.

2012 Chevy Corvette Z06 LS7's engine. (Photo: Chevrolet)

As far as I can tell, there are three explanations that define the differences between a small and a big block. Here goes:

1- A Big block is simply physically bigger. The mildly trained naked eye will notice the sheer girth of the engine block. Simple. Big blocks were used for big power; the extra material allowed for more cooling, larger oil passages and obviously enough, more meat equals better durability.

2- What defines Big from Small is stroke, the up-down motion the piston makes inside the cylinder. This is not visible but it goes like this: short strokes = small blocks and long strokes = big blocks. To me, this ties in with another answer which states that V-shaped blocks are Small and Y-shaped blocks are Big. The Y-shape would theoretically allow the connecting rod to travel further down in the block, increasing stroke.

3- Small or Big, it has nothing to do with the block. The answer lies in the engine heads and the valve arrangement type. Big blocks had a canted valve setup (called porcupine) which was instrumental in making more horsepower. Small blocks did not.

I set off writing this blog with the intention of answering the question but now I've got more questions than answers. Is there anyone out there that can clarify this issue? We'd love for you to add a comment or twelve at the bottom of this article.

Trust me, you'd be helping many so-called gearheads (including me) out there sound and feel better. I thank you in advance.

By the way, the largest current small block V8 engine is Chevy's 427 (7.0L) LS7 found in the Corvette Z06.

By Mathieu St-Pierre,

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