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How much HP does a Chevy 400 make?

The Chevy 400 typically produced about 350 horsepower in its peak years when GM listed gross ratings.

Over its production run, horsepower varied widely due to rating standards (gross vs net), model, and mechanical condition. This article outlines the range you might see and explains the factors that drive differences.

What is the Chevy 400?

The term Chevy 400 refers to Chevrolet's 400 cubic inch V8, a member of the small-block family introduced in 1970 and used through the late 1970s and into 1980. It displaced 6.6 liters and was popular in performance-oriented cars of the era, such as the Chevelle, Monte Carlo, El Camino, and others. Because GM used different rating methods over the years, horsepower numbers can be confusing if you compare a 1970s gross figure to a 1980s net figure.

Estimated horsepower by era and rating style

Power figures changed as GM shifted from gross horsepower in the early 1970s to net horsepower in the mid- to late-1970s, and because performance packages varied widely. The following ranges reflect typical configurations rather than a single exact number.

1970–1972: roughly 350–370 horsepower (gross, factory spec)

1973–1974: roughly 250–275 horsepower (net, factory spec, emission-compliant)

1975–1980: roughly 180–210 horsepower (net, emission-compliant; output varied with compression, cams, and tuning)

Note: These are generalized ranges. Specific applications, such as high-performance options or aftermarket work, could push output higher or lower. Always check the exact factory rating for the model year and trim you’re interested in, or verify with a dynamometer for a precise measurement.

What affects horsepower on a Chevy 400?

Several factors determine the exact horsepower of a Chevy 400, including the engine's mechanical condition, tuning, and equipment. Key influences include:

Compression ratio and camshaft profile

Induction system (carburetor vs. intake manifold and carb tuning; later EFI in some recipes)

Exhaust system and exhaust restrictions

Ignition timing and fuel delivery calibration

Emission-control equipment and EPA-era changes

Engine wear, maintenance history, and overall health

In practice, even cars with the same displacement could show noticeable horsepower differences based on these factors. A properly tuned 400 could approach the higher end of its era’s range, while a tired or restricted engine would fall toward the lower end.

How to verify the horsepower on a given Chevy 400

To determine the exact horsepower of a particular Chevy 400, you can use several approaches, depending on what information is available and how precise you want to be.

Consult the original factory specifications for the car and year (sales brochures, service manuals, or dealer documents).

Check the VIN-derived trim codes and RPO (Regular Production Option) sheet for engine and rating information.

Have the engine dyno-tested under controlled conditions to get a current horsepower figure.

Review service receipts for any major work that would affect power, such as cam, intake, or exhaust changes.

Because aftermarket work and minor changes can significantly alter power output, dyno testing remains the most reliable method for a current, precise number.

Summary

The Chevy 400’s horsepower varied significantly over its production life. In the early 1970s it often produced roughly 350–370 hp using gross ratings; by the mid-to-late 1970s, as GM transitioned to net horsepower ratings, output commonly fell to about 250–275 hp, with later examples in the 180–210 hp range due to emissions and tuning. Real-world numbers depend on year, model, and how the engine was built and setup. For a precise figure, consult factory documentation or perform a dyno test.

Why is a 383 better than a 400?

Through completely different engineering approaches. The 383 stroker delivered its power through aggressive bore. And stroke combinations that maximized breathing efficiency.

How much HP can a 400 SBC make?

A 400 small block Chevy (SBC) can make anywhere from 150–260 horsepower in stock form, but highly modified versions can produce 500 to over 1,000 horsepower. The final output depends entirely on the quality and type of modifications, such as adding better heads, a different cam, and other performance parts, with power adders like supercharging and turbocharging leading to significantly higher numbers.
You can watch this video to see a 400 SBC make over 500 horsepower: 52sZHP GarageYouTube · Mar 21, 2022
Stock vs. modified horsepower

Stock: Factory 400 SBC engines typically produced between 150 and 260 horsepower, depending on the specific model year and application.
Modified: Modifications allow for dramatic increases in horsepower.
- Mild to moderate builds: A lightly modified 400 SBC (e.g., with an aftermarket cam and heads) can make around 375 to 450 horsepower.
- Aggressive builds: With more aggressive parts, it's possible to exceed 500 horsepower, and with more extreme setups, even reach 600 or 1,000+ horsepower, especially with power adders like turbochargers or superchargers.

This video explains how a 400 SBC can reach over 600 horsepower: 57sRichard HoldenerYouTube · Aug 30, 2023
Key factors in determining horsepower

Cylinder heads: The stock heads are a major restriction. Upgrading to better flowing heads is one of the most significant improvements you can make.
Camshaft: A more aggressive cam with higher lift and duration will increase horsepower, but also requires other supporting modifications to work effectively.
Compression ratio: Increasing the compression ratio will boost power, but requires more performance-oriented parts and can limit the fuel you can use.
Power adders: Forced induction systems like superchargers or turbochargers can drastically increase horsepower, allowing a less modified engine to produce much more power.
Tuning and other parts: Proper tuning of the ignition and fuel systems, along with other components like exhaust and intake manifolds, is crucial for achieving maximum power and efficiency.

How much HP does a 400 big block have?

A stock Chrysler or Ford 400 big block engine typically produces 160–260 horsepower, but performance builds can achieve 400+ horsepower, with some custom builds reaching over 500 or even 700 horsepower. Stock horsepower varies by year and application (e.g., car, truck, or motorhome) and declined due to emissions controls over time.

Stock horsepower ratings

Chrysler 400: Factory ratings ranged from 170 hp for the two-barrel version to 260 hp for the high-performance four-barrel/dual-exhaust model.
Ford 400M: Produced between 160 and 180 horsepower in stock trim, according to Facebook users.
Chevrolet 409: While not a 400 cubic inch engine, this similar engine is often mentioned. In 1963, a high-performance version produced 425 hp.

High-performance builds

Custom builds: By using aftermarket parts, high-performance builds can achieve significantly more horsepower.
400+ hp: It is common to build a 400ci engine to exceed 400 horsepower with a combination of updated components.
500+ hp: Builds are available that target and achieve 500 hp or more.
700+ hp: Extreme applications, such as pulling trucks, can reach well over 700 horsepower.

This video shows how to build a 400 hp Mopar engine: 54sJustMoparJoeYouTube · Jun 1, 2022

What's the difference between a Chevy 350 and a 400?

The Chevy 350 has more readily available aftermarket support and parts, while the 400 offers a larger displacement (400 vs 350 cubic inches400 vs 350 cubic inches400 vs 350 cubic inches) and more low-end torque, though it can be more prone to overheating if not properly modified. Key internal differences include the 400's larger bore (4.125 inches vs 4.0 inches4.125 inches vs 4.0 inches4.125 inches vs 4.0 inches), longer stroke (3.75 inches vs 3.48 inches3.75 inches vs 3.48 inches3.75 inches vs 3.48 inches), and shorter connecting rods. The 400 also uses Siamese cylinders, requires different head gaskets, and is externally balanced, unlike the internally balanced 350.

This video explains the differences between Chevy 350 and 400 engines: 53sMyvintageiron7512YouTube · Feb 12, 2023
Chevy 400 vs. 350 comparison

Feature	Chevy 400	Chevy 350
Displacement	400 cubic inches400 cubic inches400 cubic inches	350 cubic inches350 cubic inches350 cubic inches
Bore	4.125 inches4.125 inches4.125 inches	4.0 inches4.0 inches4.0 inches
Stroke	3.75 inches3.75 inches3.75 inches	3.48 inches3.48 inches3.48 inches
Rod Length	Shorter (approx. 5.565 inches5.565 inches5.565 inches)	Longer (approx. 5.7 inches5.7 inches5.7 inches)
Cylinders	Siamese (no cooling passages between center cylinders)	Standard
Balancing	Externally balanced	Internally balanced
Aftermarket Support	Less common	Very common
Torque	Higher low-end torque	Lower low-end torque
Potential Issues	Can overheat if steam holes are not drilled in heads	—

For high torque: The 400's larger displacement provides more low-end power and torque, making it ideal for heavy-duty applications like trucks.
For easier modifications: The 350 has a vast aftermarket parts selection, which can simplify and lower the cost of performance upgrades.
For cooling: Any 400 engine swap requires ensuring the cylinder heads have steam holes to prevent overheating, a modification often overlooked.
For stroker builds: The 400's crankshaft is the same length as the one used to build a 383 "stroker" small block from a 350. Using a 400 block can be a cheaper way to get the larger displacement.

Kevin Bennett

Company Owner

Kevin Bennet is the founder and owner of Kevin's Autos, a leading automotive service provider in Australia. With a deep commitment to customer satisfaction and years of industry expertise, Kevin uses his blog to answer the most common questions posed by his customers. From maintenance tips to troubleshooting advice, Kevin's articles are designed to empower drivers with the knowledge they need to keep their vehicles running smoothly and safely.