What Are Big Block and Small Block Engines?
Big block and small block are frequent descriptors of V8 pushrod engines, also called overhead valve engines. Though big-block engines are significantly larger than their small-block brethren, the true difference between these two is more about displacement, bore, and stroke than strictly size. Typically, big-block engines have displacements of greater than 400 cubic inches and small block engines have a smaller displacement.
But because this is the automotive world, and nothing can be quite that simple, there are a few exceptions to that rule that require a slightly more in-depth explanation. There are engines with large displacements that are frequently referred to as small block due to the design of the valves and layout of the cylinders of the engine. The Chevy 396 engine is an example of an engine that has a displacement under 400 cubic inches but is considered a “big block” due to its architecture.
Engine Displacement: Only Part of the Answer
Displacement is a measurement of the volume of an engine’s pistons. It can be referred to in cubic inches or in liters. Though displacement doesn’t always relate directly to power, a larger displacement does mean that more air and fuel can be taken in, which does usually correlate to more power. As some enthusiasts say “there’s no replacement for displacement.”
400 cubic inches is equivalent to 6.6L, and you can use this engine size chart to convert easily between the two.
When talking about older cars, it’s common to use cubic inches to measure the volume since that’s how it would have been measured at the time and it doesn’t always convert neatly to liters. Plus, many models of cars actually used their displacement as part of their name, like the Boss 429, which came with a big block v8 engine that had a 429 cubic inch displacement.
Calculating volume requires two measurements that impact whether an engine is classified as a small or big block engine: Bore and stroke. Though displacement is often thought of as the only delineation between small and big block engines, bore and stroke are equally important and is usually the major difference when we talk about an engine with a huge displacement that has “small-block architecture.”
In each cylinder of an engine is a piston, and the distance that piston has to travel up and down is referred to as “stroke.”
Small stroke equals small block, long strokes equal big blocks. Typically long strokes result in more torque while short strokes make quicker revving possible.
Bore size relates to the diameter of an engine’s cylinders. Big bores equal better breathing, and small bores create more pressure, equaling more torque. Smaller bores do create limitations on red line numbers though, which many enthusiasts find frustrating, but that is ideal for the large trucks that big block engines were first designed for.
So, while a race car will have a small stroke to bore ratio, a large truck will ideally have a large stroke to bore ratio.
Understanding Block Engines
Though almost all modern engines are part of the “monobloc” family that was introduced in the early 1900s, that isn’t quite what people mean when they’re talking about block engines. Overhead camshaft engines are also monoblocs, but they aren’t frequently referred to as big or small. When people refer to block engines, they’re usually specifically referring to overhead-valve, or pushrod, V8 engines designed after 1955.
Mustangs switched from overhead valve to overhead camshaft engines in the late ‘90s, but many older Mustangs came with small or big block V8s. General Motors now holds the title of largest pushrod engine manufacturer, since nearly every other company has shifted to overhead cam designs.
Pushrod engines have benefits that make them desirable for many. They’re significantly easier to work on than an overhead cam engine, and the engine sits lower in the car. Because a significant part of a vehicle’s weight is comprised of the engine and its components, this gives the car a lower center of gravity, which is desirable for several reasons related to performance and safety. They also have an easier time getting low-end torque, which a lot of drivers just like the feel of.
Small Block Engines
Referred to sometimes as “mouse motors,” the small block engine as we know it was introduced in the mid-50s by Chevrolet. The first one was a 265 cubic inch engine popularly called “Turbo-Fire” and it was offered for Bel Airs and Corvettes. Many have credited this engine with “saving” the Corvette, but that’s a pretty inflammatory remark in some circles. What’s indisputable is that changing to the small-block V8 improved the Corvette’s 0-60 mph time by 1.5 seconds.
The Turbo-Fire engine featured a 4.4-inch bore spacing that is considered one of the hallmarks of small block engines still today. Additionally, it had a 3.75” bore and a 3” stroke. Small block absolutely seemed like the right word for it. In 1955, its 162-horsepower output seemed phenomenal, and it had a solid 257 lb-ft of torque.
In 2011, GM manufactured it’s 100 millionth small block, so you might say that it was successful. It was estimated that if you lined up all of the small block engines produced by 2011 they would be able to wrap around the earth. Twice.
Small block engines are still utilized today in many of Chevy’s vehicles. Chevrolet is manufacturing its fourth generation of small block V8 engines currently. Because these small blocks can accommodate displacement ranges of up to 454 cubic inches, they’ve phased out big block engines entirely and are using these small blocks on everything from the Corvette family to Chevy trucks.
Additionally, classic small block engines are frequently used in classic vehicle restoration because their small size allows them to fit into a wide range of engine bays.
Ford didn’t start manufacturing small block V8 engines until 1961. The first one was introduced in the Fairlane, but that engine eventually became the basis for not only the Windsor but also for the HiPo engine that Shelby used for the first GT350.
Small Block Engine
Also referred to as “Rats” and “Turbo-Jet” motors, names that are derived from the nicknames of the small block V8, the big block engines debuted after the small-blocks. In the late 1950s, Chevrolet decided they needed an engine more powerful than their small block engines at the time were capable of being. Hence, the big block. The big block was used in trucks and passenger cars, big vehicles that needed a lot of power.
Chevrolet’s first big block was introduced in 1958 and referred to as the “W” series. It had offset valves and scalloped rocker covers features that many big blocks kept.
Ford didn’t join in on the big block fun until ’68. Some experts will say that there aren’t big blocks being produced anymore because large engines that are being manufactured are manufactured as oversized-small blocks.
GM manufactured the last of the L18 big block engines in December 2009. Since then, all the V8s produced by GM have been small block engines with big displacements. With modern materials, it’s possible to create materials that are strong enough that even with a large bore size they don’t need to be particularly large, and for performance a lighter engine that can be equally powerful is always a good thing.
But because many love the way big block engines sound and feel, or because they want to restore a vehicle accurately, the aftermarket makes it possible for enthusiasts to build a big block of their own if they so desire, without using a single part from GM.
Big Block Engine
The displacement in a small block and a big block can be the same, and there’s obviously significant overlap. As of 2009, only new small-blocks are being produced (albeit with a rather large displacement). The features that will determine whether an engine is viewed as a big block or small block relate to the physical proportions, the other engines that are in the same “family” and use the same parts, and the shape and placement of the valves.
Big blocks are squarer, and typically will have cylinders placed further away from each other. Though both engine styles are V-shaped, in a big block engine, that V looks more like a “Y” than not because of the additional space needed.
It’s possible that you’ve heard a big block engine referred to as a “porcupine.” This is a fairly apt description and is caused by a canted valve setup that offers a lot of power but does create a fairly scattered appearance with valves seemingly going everywhere like the quills on a porcupine.
For the time, the canted valve setup was an innovative way to allow the engine to breathe and generate power. Now, we know that there are significantly easier and more efficient ways to create additional airflow for an engine. This is part of the reason why modern small block engines will almost always beat out vintage stock big block engines in a straight horsepower contest.
Of course, there’s nothing saying you need to keep a big block stock. Increasing the bore sizing of a big block engine will allow it to breathe more easily, increasing its power significantly.
- Big block engines are physically larger and heavier.
- Big block engines typically have longer strokes and smaller bores.
- Though displacement is a good indicator, it isn't the definitive answer on big vs small.
- Though initially big blocks were designed for large cars and light trucks, that has changed.
Sources Small Block vs Big Bock-A Game of Rat and Mouse, Motortrend | Small Block Fast Facts, General Motors | This is the Difference Between Small and Big Blocks, Hagerty | Ford Big Block Engine Parts Interchange, CarTech | No Replacement for Displacement, Reher Morrison |Image Credit | Creative Commons