A 400 small-block Chevy is a mid-sized V8 that sits between the popular 350 and the larger 454 big-block

The 400 small-block (also called a 400 SBC) is a V8 engine Chevrolet produced from 1970 to 1980. It has a 400 cubic-inch displacement, which makes it larger than the 350 but still part of the small-block family — meaning it shares the same basic bolt patterns and mounting points as smaller Chevy V8s. If you own a vehicle from that era or are considering an engine swap, understanding what a 400 can and cannot do will help you decide whether it fits your needs and budget.

The 400 was designed to bridge a gap: drivers wanted more power than a 350 offered, but the big-block 454 was expensive, heavy, and thirsty. The 400 delivered more torque than a 350 without the fuel consumption penalty of a big-block. However, it was never as popular as either engine it sat between, which affects parts availability and resale value today.

Key Takeaways

  • A 400 small-block shares mounting points with 350s and other small-blocks, making it a practical swap into older Chevrolet vehicles without major frame or transmission modifications.
  • Factory 400s produced between 1970 and 1980 ranged from 265 to 375 horsepower depending on the year and carburetor setup, with most examples in the 300–330 range.
  • Used 400 blocks cost between $400 and $1,200 depending on condition and whether the engine is complete or just the block, while a fully rebuilt 400 typically runs $2,500 to $4,500.
  • The 400 produces more low-end torque than a 350 but has a longer stroke that can limit maximum RPM, making it better suited for street driving than high-RPM racing.
  • Parts for a 400 are harder to find than 350 parts because fewer were made, and some performance upgrades designed for 350s do not fit without modification.

Factory horsepower and torque ratings by year

Chevrolet's 400 small-block output varied significantly depending on the model year and whether the engine was equipped with a two-barrel or four-barrel carburetor. Early versions (1970–1972) produced around 265 to 300 horsepower. Mid-production years (1973–1976) typically ranged from 290 to 330 horsepower as emissions controls tightened. The final years (1977–1980) saw output drop again to around 265 to 305 horsepower as catalytic converters and air injection systems became standard.

Torque figures were the 400's stronger suit. Most factory 400s produced between 400 and 460 pound-feet of torque, with peak torque arriving at lower RPMs (around 2,400 to 3,200) compared to a 350. This made the 400 feel responsive in everyday driving and towing, even if the top-end horsepower numbers did not look impressive on paper. A stock 400 will not rev as high as a 350 — the longer stroke limits safe RPM to around 5,500 to 6,000 for most stock blocks — which is why it never became popular in racing circles.

What a used 400 block costs

A bare 400 block (just the casting, no internals) typically sells for $300 to $800 depending on condition, whether it has been bored or damaged, and your location. A complete short-block (block, crankshaft, connecting rods, and pistons) runs $600 to $1,500. A long-block (short-block plus cylinder head, valves, and timing cover) costs $1,200 to $2,200.

A fully rebuilt 400 engine ready to bolt in and start ranges from $2,500 to $4,500, depending on whether the machine shop performed a basic rebuild or a performance build with upgraded internals. Machine work itself — boring, honing, and line-boring — typically costs $400 to $800 on top of the core price. Prices vary by region and the reputation of the seller or shop; a 400 from a reputable engine rebuilder will cost more than a used pull from a junkyard but comes with a warranty and known history.

Small-block compatibility and what you can swap it into

The 400 shares the same bolt pattern and mounting points as the 350, 327, 305, and other Chevy small-blocks. This means if you have a vehicle that originally came with a small-block V8, a 400 will bolt into the same engine bay with minimal modification. The transmission, radiator, and exhaust manifolds from a 350 will usually work with a 400, though you may need to verify specific years and models with a mechanic.

The 400 is heavier than a 350 (roughly 50 pounds more) due to its larger displacement, so front-end weight distribution changes slightly. This is rarely a problem in street cars but matters if you are building a race car or a vehicle where weight balance is critical. The longer stroke also means the engine sits slightly lower in the block, which can affect hood clearance in some tight engine bays — measure before you commit to the swap.

The 400 will not fit into vehicles designed for inline-six engines or big-block V8s without significant fabrication. It is a small-block swap only, and only into vehicles that originally accepted small-blocks.

Performance potential and realistic power gains

A stock 400 makes more torque than a stock 350 at lower RPMs, but the difference in horsepower is modest — usually 20 to 40 horses depending on the year. If you are swapping a 400 into a vehicle that originally had a smaller engine, you will feel the torque increase more than the horsepower increase. Acceleration off the line and pulling power improve noticeably; top-end speed does not change as much.

A mildly modified 400 (better carburetor, intake manifold, and exhaust) can reach 350 to 380 horsepower. A more aggressive build with a performance cam, ported heads, and a higher-compression piston set can push 400 to 450 horsepower, but you will need to upgrade the fuel system, ignition, and cooling to handle it. A heavily modified 400 can exceed 450 horsepower, but at that point you are spending money that would buy you a better-performing 350 or 383 small-block from a performance builder.

The 400's long stroke limits its ability to rev safely. Most stock blocks should not exceed 5,500 to 6,000 RPM without risk of internal damage. This makes the 400 a poor choice for high-RPM racing but an excellent choice for street driving, towing, and low-RPM torque applications.

Parts availability and sourcing challenges

The 400 was produced in smaller numbers than the 350, which means fewer parts are readily available through major suppliers. Common items like oil pans, water pumps, and gasket sets are still obtainable, but specialty parts like performance camshafts, intake manifolds, and cylinder heads designed specifically for a 400 are harder to find. Many performance parts marketed for "small-blocks" are designed around the 350 and may not fit a 400 without modification.

Crankshafts, connecting rods, and pistons for a 400 are different from 350 parts and are not interchangeable. If you need internal machine work, you must find a shop experienced with 400s or be prepared to pay extra for custom work. Online forums and specialty Chevy engine suppliers are your best sources for 400-specific parts; local auto parts stores often cannot help.

Junkyard 400s are becoming rarer as older vehicles are scrapped, so if you find a good used 400, buying it sooner rather than later is usually the smarter move. Prices for used 400s have been creeping up as interest in vintage Chevy engines has grown.

When a 400 makes sense versus other small-block options

A 400 is the right choice if you want more torque than a 350 without the cost and complexity of a big-block swap, and you have a vehicle that originally came with a small-block. It is also a good option if you find a complete, low-mileage 400 at a good price and want to avoid the machine work required to rebuild a worn 350.

A 400 is not the right choice if you are building a high-RPM engine, planning to race, or need maximum horsepower per dollar spent. In those cases, a 350 with performance modifications or a 383 stroker (which combines a 350 block with a 400 crankshaft) will serve you better. A 383 stroker actually gives you the best of both worlds — the RPM capability of a 350 with more displacement and torque — but requires machine work and costs more upfront.

Frequently Asked Questions

Can I put a 400 in a car that had a 350?

Yes. The 400 uses the same bolt pattern, motor mounts, and transmission coupling as a 350. You will need to verify that your specific vehicle year and model are compatible, but in most cases a 400 will bolt directly into a 350 engine bay with no frame or transmission modifications.

How much horsepower does a stock 400 make?

Factory 400s ranged from 265 to 375 horsepower depending on the year and carburetor type, with most examples between 300 and 330 horsepower. Torque was the stronger suit, typically 400 to 460 pound-feet at lower RPMs.

Why is a 400 harder to find parts for than a 350?

Chevrolet produced far fewer 400s than 350s between 1970 and 1980, so fewer used parts are available in junkyards and from suppliers. Many performance parts are designed around the 350 and do not fit a 400 without modification.

What is the maximum safe RPM for a 400 small-block?

Most stock 400 blocks should not exceed 5,500 to 6,000 RPM without risk of internal damage. The long stroke limits high-RPM capability, making the 400 better suited for street driving and low-RPM torque than racing.

Is a 400 better than a 383 stroker?

A 383 stroker (350 block with 400 crankshaft) offers more RPM capability and similar torque, but requires machine work and costs more. A 400 is simpler and cheaper if you find a complete used engine, but the 383 is the better choice for performance-oriented builds.