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 2 comments

  • I can't take it anymore so I'm commenting on a 4 year old blog thread that is probably dead. Mis-information run rampant and this pops up when you search for differences between small blocks and big blocks. "Small Block" versus "Big Block" refers to the cylinder block casting. The first original numbered answer is close to correct, but the small block chevy is bigger than it's contemporary Y-block fords. Small was in relation to Chevy's other V-8 casting at the time, the W-block (348, 409, and 427 cubic inch displacements available up until 1963, not to be confused with the 'modern' Chevy big block available in displacements from 366 to 540 cubic inches - including the famous 427 big block (but there is also a 427 W-block, and now a 427 small block). The block casting is the big piece of metal that contains the pistons, crank, etc - you can put different size pistons, cranks, even cylinder heads, but the outer dimensions of the casting and location of bore centerlines have remained common in the Chevy small block due it's longetivity and parts interchangeability. Reasons 2 stated above is incorrect as you can have "small" and "big" blocks with or without Y-block. In fact even the original first generation big block chevy is not a Y-block casting (the block casting does not extend beyond crank centerline). Head design doesn't have anything to do with small block versus big block as all sorts of cylinder heads have been bolted to small block chevy castings and the original big block chevy through 1963 had straight valves (no 'porcupine').

    • Oops accidentally hit the submit button before correcting my typos and concluding: so it's cylinder block casting that distinguishes SBC from BBC. They castings differ in size but not much - you might not notice the 4.84 versus 4.4" bore spacing of the big block versus small block unless they were not next to each other, but and more obviously their differing bolt patterns making them easy to distinguish. The SBC was called small at the time because it was smaller than it's contemporary bigger blocks and thus was lighter weight, but it became legendary because of it's performance to weight ratio, durability, and it's production duration which resulted in extreme interchangeability: The original 265 cubic inch 1955 SBC has interchangability with the 2000's LT1 and Vortec engine production and still shares the same block casting dimensions with the modern 427 cubic inch LS7 small block dimensions (including 4.40" bore spacing).

    • Reply
  • 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.