Comparison between large-block engines and small-block engines

Since the invention of the internal combustion engine, the pursuit of power has been the primary focus of its development and advancement over the years. Various cylinder counts, cylinder configurations, displacement, bore, and stroke lengths have all been designed to maximize horsepower and torque. It is safe to say that the most widely used engine layout is the powerful V8 engine, which is why it is used in nearly all modern sports cars, from the Ford Mustang to the Chevrolet Corvette. The V8 engine is the perfect combination of cylinder count, physical size, and output power. In the V8 engine realm, there are two sizes: big block and small block.

This comparison is not only based on technical information but also provides some historical context to help better understand the differences and applications between the two engine blocks and how their respective manufacturers classify them.

Explanation of Big Block vs. Small Block

Defining the Differences

Starting in the 1950s, the terms “big block” and “small block” began to be used to distinguish engine displacement. By the 1960s, manufacturers began using these terms in marketing campaigns, and the muscle car era followed. At this point, “big block” and “small block” had become household terms, and if you were a car enthusiast, the type of car you drove could determine your reputation.

What is the difference between the two? The mystery has been officially revealed, but there are still some blurred lines in the truth. The key difference between these two cylinder blocks lies in what is known as the “bore center distance.” The bore center distance refers to the distance between the centerlines of adjacent cylinder bores in the engine block. Since the bore center distance is larger in a big-block engine, there is more space to accommodate a larger bore diameter. Conversely, the bore center distance is smaller in a small-block engine, so there is less space to accommodate a larger bore diameter. This is the primary factor determining whether a cylinder block is a big-block or a small-block. While cubic inches are commonly used to classify engines, this measurement method can be misleading. Cubic inches are determined by the engine's bore and stroke, and the engine's bore is largely dependent on the bore center distance. There is no standard bore center distance to classify an engine as large-block or small-block; classification is set by the manufacturer, but typically, large-block engines have a bore center distance exceeding 4.5 inches.

Common engine bore center distances

Large block

Small block

Chevrolet

4.84 inches

4.4 inches

Ford FE

4.63 inches

Not applicable

Ford

4.9 inches

4.38 inches

Chrysler

4.8 inches

4.46 inches

Large engines, large power

Large cylinder blocks have larger bore diameters and longer strokes, resulting in larger cylinder volumes. This is measured in cubic inches (ci). In addition to the bore center distance measurement for large cylinder blocks, most people consider an engine with a displacement exceeding 400 cubic inches (6.6 liters) to be a large cylinder block. However, this boundary is also somewhat vague. For example, the Oldsmobile 403 cubic inch V8 engine is referred to as a small-block by Oldsmobile, while the Chevrolet 396/402 is considered a big-block. Due to its larger bore and stroke, a big-block can generate massive torque at lower RPM (revolutions per minute).

At its core, any engine, regardless of size, is simply an air pump. To supply air to larger engines, big-block engines are equipped with larger intake and exhaust valves to deliver more air. A larger bore allows more air/fuel to enter the combustion chamber for compression and ignition. Greater explosive force means greater power. A longer stroke acts like a lever or long handle on the crankshaft, enabling the engine to produce greater torque per revolution. This is why you see many drag racing cars using large-bore engines, or why older gas-powered medium and heavy-duty commercial trucks and buses also use large-bore engines.

During the muscle car era, large-bore engines became a popular choice for passenger vehicles, as manufacturers' marketing strategies made large-bore engines synonymous with high power and quarter-mile performance. This directly impacted the sales of muscle cars equipped with large-displacement engines, while smaller-displacement engines were used in entry-level muscle cars, standard engine options, and even economy sedans. Some of the most popular large-displacement engines had easily recognizable nicknames, such as “Hemi,” which refers to a hemispherical combustion chamber cylinder head design used by Chrysler on its popular 426 cubic inch large-displacement engine. The Big Three—General Motors, Chrysler, and Ford—were the main competitors in the muscle car era's street horsepower wars. However, big-block engines were not exclusively produced for the large cars of the 1950s and the muscle cars of the 1960s and 1970s.

Don't forget trucks!

Big-block engines were also widely used in trucks, ranging from large commercial trucks and buses to consumer-grade pickup trucks. Large-displacement engines are ideal for towing and hauling, as they can fully utilize their strong low-end torque, making them an excellent choice for moving heavy loads. Today, the efficiency of large-displacement engines is no longer what it once was. There are many reasons for this, such as increased emissions, higher Corporate Average Fuel Economy (CAFE) standards, and the operational costs of commercial trucks. It has been proven that diesel engines are significantly more fuel-efficient than large-displacement gasoline engines.

Gone but not forgotten

In terms of current usage, large-displacement engines are largely obsolete, though some models still feature larger-displacement engines. The horsepower race among manufacturers continues, as the traditional Big Three automakers have introduced some powerful engines in recent years, such as the LS7. The LS7 is a 7.0-liter, 427 cubic inch V8 engine based on the popular small-displacement LS engine platform, capable of producing over 500 horsepower. While medium and heavy-duty trucks may have fully transitioned to diesel, the heavy-duty pickup truck market still offers some excellent large-displacement options, even if they are no longer sold as large-displacement engines. The Ram 6.4-liter and Ford 7.3-liter V8 engines are both based on smaller engines, so manufacturers do not classify them or market them as big-block engines. Until its discontinuation in 2009, General Motors offered an 8.1-liter 496 cubic inch V8 engine in its heavy-duty pickup trucks.

Big-block engines

Advantages and disadvantages

High power at low RPM

No need for extensive upgrades to achieve high power

Excellent exhaust sound

High torque

Always low on oil

High construction and maintenance costs

Heavy

Can produce similar power with smaller engines, especially with power adders

Small size, big engine

Smaller but still powerful

While large-block engines may be massive in size, small-block engines can fill all other gaps and meet all requirements. Before the advent of small-block engines, manufacturers used various inline engines. These engines were powerful, cost-effective to manufacture, and easy to mass-produce. Ford did have a flat-head V8 engine, which was popular at the time due to its high power output. There were other V8 engines in that era, but they were not considered small-block. In 1955, Chevrolet introduced the first small-block engine. This was a 265 cubic inch V8 engine designed by General Motors Chief Engineer Ed Cole and his team. Soon after, other manufacturers followed suit, introducing their own small-block V8 engines.

When measured solely by cubic inches, an engine is considered small-block if its displacement is below 400 cubic inches (6.6 liters). As is well known, this is a gray area. For example, the Chrysler 383 cubic inch V8 engine is classified as a big-block when its displacement is below 400 cubic inches. This underscores why bore center distance measurement is so crucial for accurately classifying engine block sizes. Like big-blocks, different manufacturers offer various sizes and versions. Small-block engines are widely used in most models of passenger cars and light trucks. The physical dimensions of a small-block engine are indeed different, but its bore is also smaller, and its stroke is shorter. These characteristics may result in a lower cubic inch count, but due to its smaller overall size and lighter weight, the small-block engine offers a high power-to-weight ratio. The small-block engine can operate at high RPMs, making it relatively easy to generate significant horsepower. Basically, the higher the engine speed, the more combustion cycles occur, resulting in more power strokes to drive the crankshaft rotation. While large-displacement engines were once considered the kings of the streets and racetracks, small-displacement engines are equally impressive.

The little soldier marches on

Over time, federal regulations have also had a significant impact on small-block engines. The main difference is that small-block engines survived the smog era, while large-block engines were largely phased out. However, this was not entirely due to emissions regulations. Advances in engine technology brought about innovations such as fuel injection and computerized engine control. Aluminum cylinder blocks and heads also became mainstream, significantly reducing weight. Ultimately, small-displacement V8 engines became the largest engines in most vehicles. Large-displacement engines remain a popular choice for heavy-duty pickup truck buyers, as diesel technology has not yet matured and offers no significant advantages over gasoline-powered large-displacement engines.

Currently, small-displacement engines remain active and incorporate more advanced technologies, such as direct fuel injection and variable valve timing. Modern small-block engines can easily produce the power of large-block engines without the bulk and weight. Although there are far fewer models equipped with small-block engines now than before, they are primarily used in half-ton pickups and new muscle cars. Diesel technology has made significant strides in power, reliability, and ease of use, leading to diesel sales far exceeding those of gasoline-powered heavy-duty pickups. Large-displacement small-block V8 engines remain the standard configuration for heavy-duty pickups.

Small Engines

Advantages and Disadvantages

Can achieve higher RPMs

Lightweight with a high power-to-weight ratio

Improved fuel economy

Cost-effective power source

Compact size makes it suitable for a variety of applications

Not suitable for truly heavy-duty applications

Looks less intimidating under the hood

Requires significant modifications to achieve maximum power