The 400 small block is a V8 engine with 400 cubic inches of displacement, originally built by Chevrolet and later by other manufacturers

A 400 small block refers to an eight-cylinder engine with a total displacement of 400 cubic inches—roughly 6.6 liters. Chevrolet introduced the 400 small block in 1970 as part of its Chevrolet V8 family, and it remained in production through the mid-1980s. The engine sits in the middle of Chevrolet's small block lineup, larger than the 350 cubic inch version but smaller than the big block engines that Chevrolet also offered.

The term "small block" distinguishes it from Chevrolet's big block engines, which had different dimensions, mounting points, and performance characteristics. A 400 small block can physically fit into engine bays designed for smaller Chevrolet V8s, making it a popular swap for older vehicles. The engine was never as common as the 350 or as sought-after as the 427 big block, which affects both availability and pricing in the used parts market today.

Key Takeaways

  • The 400 small block displaces 400 cubic inches and was produced by Chevrolet from 1970 to the mid-1980s as a mid-range V8 option.
  • It uses the same bolt pattern and mounting points as other Chevrolet small blocks, making it a direct replacement in vehicles originally equipped with 350 or smaller engines.
  • Factory 400 small blocks produced lower horsepower than comparable big block engines, typically ranging from 150 to 265 horsepower depending on the year and fuel system.
  • The 400 small block is less common in the used parts market than the 350, which can make finding original components more difficult and expensive.
  • Modern performance builders can modify a 400 small block to produce significantly more power than the factory version through head work, intake changes, and fuel system upgrades.

How the 400 small block compares to other Chevrolet V8 sizes

Chevrolet's small block family includes the 262, 267, 283, 305, 327, 350, and 400 cubic inch versions. The 400 sits near the top of that range. A 350 small block, which was far more common, produces similar or sometimes greater horsepower than a 400 despite the smaller displacement—a result of different bore and stroke combinations and varying compression ratios across model years.

The big block engines—such as the 396, 427, and 454—are physically larger and heavier, with different block casting, heads, and intake manifolds. A 400 small block cannot be directly swapped into a vehicle designed for a big block without significant modification to engine mounts and cooling systems. Conversely, a 400 small block fits into any vehicle that originally held a 350 or smaller small block, which is why it remains popular for engine swaps.

In terms of raw displacement, a 400 cubic inch engine produces more torque potential than a 350 at lower engine speeds, but factory versions often underperformed because Chevrolet prioritized fuel economy and emissions compliance during the 1970s and early 1980s. Modern builders can extract more power from a 400 than Chevrolet's original engineers did.

Factory horsepower and torque ratings across production years

Chevrolet's 400 small block horsepower varied significantly depending on the model year, fuel system, and intended use. In 1970, the first year of production, the 400 was rated at 265 horsepower. By the mid-1970s, as emissions standards tightened, horsepower ratings dropped to around 150 to 180 horsepower for most applications. The engine was never offered with the same performance focus as the 350 or big blocks.

Torque ratings followed a similar pattern. Early 400 small blocks produced around 380 foot-pounds of torque, while later versions produced 300 to 330 foot-pounds depending on the year. These figures represent net horsepower and torque—measured at the engine's output shaft after accounting for engine accessories—not gross figures, which were higher but less representative of real-world performance.

The 400 small block was never offered in high-performance variants like the 350 was. Chevrolet did not produce a fuel-injected or turbocharged 400 small block for street use, and the engine disappeared from the lineup before the era of computer-controlled fuel injection became standard.

Common uses and why the 400 small block appears in swaps today

The 400 small block was installed in mid-size and full-size Chevrolet vehicles, including Camaros, Novas, Chevelles, and Malibus, as well as Chevrolet trucks. It was never a performance icon like the 427 big block or the 350 small block, so fewer enthusiasts sought them out when new. Today, the 400 small block appears mainly in engine swaps and restoration projects.

Builders choose the 400 small block for swaps because it offers more displacement than a 350 in the same physical package. A 400 can be bored and stroked further than a 350, or fitted with modern fuel injection and ignition systems to produce substantially more power than the factory version. The cost of a used 400 small block is often lower than a 350 because demand is lower, making it an economical choice for someone building a street engine on a budget.

The 400 small block also appears in marine applications, where the extra displacement and torque can be useful. Some builders use 400 blocks as the foundation for stroker engines—a technique where the crankshaft is replaced with a longer-stroke unit to increase displacement even further.

Identifying a 400 small block and checking its condition

A 400 small block can be identified by casting numbers on the block itself, typically located on the passenger side near the oil filter or on the front of the block below the cylinder head. Chevrolet casting numbers beginning with "14" or "15" followed by additional digits indicate a 400 small block. The engine block will also have "400" stamped or cast into it, though this marking can wear away on older engines.

The intake manifold casting number also indicates displacement. A 400 small block will have a different intake manifold than a 350, though aftermarket manifolds are available for both. The cylinder head casting numbers differ as well, though heads from other small blocks can be adapted with machine work.

When inspecting a used 400 small block, look for cracks in the block or heads, corrosion inside the water jackets, and scoring or pitting on the cylinder walls. A compression test will reveal whether the rings and valves are sealing properly. If the engine has been sitting for years, the cylinders may be rusted, which can sometimes be cleaned out with honing, or may require boring to the next oversize if damage is severe.

Rebuilding and modifying a 400 small block for more power

A stock 400 small block can be rebuilt to factory specifications using standard rebuild kits, gaskets, and bearings available from automotive suppliers. A full rebuild includes new pistons, rings, bearings, gaskets, and seals. The cost varies depending on whether the block and heads need machine work, but a basic rebuild typically costs between $1,500 and $3,000 in labor and parts.

Builders who want more power than the factory version offered can upgrade the cylinder heads with larger valves and better flow characteristics, install a performance camshaft, add a higher-flow intake manifold, and upgrade the fuel system and ignition. These modifications can increase horsepower from the original 150 to 265 range to 350 to 450 horsepower or more, depending on how extensively the engine is modified and what fuel octane is used.

A 400 small block can also be bored and stroked to increase displacement to 406, 408, or even 427 cubic inches. This requires machine work on the block and a custom crankshaft, but the result is an engine that retains the small block's compact size while approaching big block displacement. These stroker engines are popular in street rods and classic car restorations.

Finding parts and determining if a 400 small block is right for your project

Parts availability for a 400 small block is lower than for a 350 small block, but most common components are still obtainable. Gasket sets, bearing kits, and basic internal parts are stocked by major automotive suppliers. Specialty parts such as original cylinder heads or intake manifolds can be harder to find and may require searching salvage yards or online marketplaces.

Aftermarket performance parts designed for small blocks—such as fuel injection kits, ignition systems, and camshafts—are usually marketed as compatible with "Chevrolet small block" engines generally, which includes the 400. However, some performance parts are optimized for the 350 and may not perform as well in a 400 without tuning adjustments.

A 400 small block makes sense for a project if you already have access to one, if cost is a primary concern, or if you want more displacement than a 350 without the size and weight of a big block. It is less ideal if you need a specific performance level that requires extensive modification, or if you prefer an engine with abundant aftermarket support and documentation.

Frequently Asked Questions

Can I put a 400 small block into a car that originally had a 350?

Yes. The 400 small block uses the same bolt pattern, mounting points, and engine bay dimensions as the 350 and other small blocks. You will need to verify that your cooling system, fuel system, and exhaust can accommodate the slightly larger engine, but the swap is mechanically straightforward.

How much horsepower does a stock 400 small block make?

Factory 400 small blocks ranged from 150 to 265 horsepower depending on the year and process. Early 1970s versions were rated higher; later versions produced less power due to emissions controls. These are net horsepower figures measured at the engine's output shaft.

Is a 400 small block better than a 350?

Not necessarily. A 400 has more displacement, which can mean more torque at lower speeds, but factory 400s often produced similar or lower horsepower than 350s. A 400 is useful if you want more displacement in the same package size, or if you plan to modify it extensively. For stock performance, a 350 is usually the better choice.

What does "small block" mean?

Small block refers to Chevrolet's compact V8 engine family, which includes displacements from 262 to 400 cubic inches. These engines are physically smaller and lighter than Chevrolet's big block engines and use different block castings and mounting points. The term distinguishes them by size category, not performance level.

Where can I find a 400 small block engine?

Used 400 small blocks are available from salvage yards, online marketplaces, and specialty engine suppliers. Prices vary based on condition and mileage. Because the 400 was less common than the 350, you may need to search multiple sources or be willing to wait for one to become available in your area.