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 in late 2011, a milestone nearly 6 decades 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. 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 Mathieu St-Pierre,

See the comment

  • Former Race Car Engineer here! It is really quite a bit simpler than that: The domestic car companies of the 50s and 60s were not the monolithic corporations that we know and love today. Instead, they were the shotgun marriages between a number of different, smaller car companies - each of whom had their own product lines. And some of the larger ones - like Chevrolet and Ford - had different teams working on similar products, effectively stovepiped. At one point, General Motors had two models of 350 CID Chevrolet motors, the 350 Pontiac, the 350 Olds, and the 350 Buick - all producing roughly the same amount of power, and none of whom were parts-compatible with any other model. All of these different engines were based on different block castings, and each casting could be made in different displacements, mostly by changing the bore size. All of these engines were roughly the same dimensions, externally - except for one. The odd man out was the small block Chevy which was physically smaller than the other motors, and accordingly, was a little lighter (actually a lot lighter). But it also could not displace as much, as the smaller block casting limited how big the bores can get. The Big Block Chevy, the Olds, the Pontiac, and the Buick could all displace 454-455 CID, where the small block topped out at 400 CID. The terms big block and small block are literally about differentiating between two separate models of Chevrolet V8s - that`s it.