The 350 engine block is the iron or aluminum casting that holds the cylinders, pistons, and crankshaft of a Chevrolet V8 engine

The block is the foundation of the entire engine. It is a single large casting with eight cylindrical holes bored into it — one for each piston. Inside the block, the crankshaft spins on main bearings, and the pistons connect to it via connecting rods. Oil passages run through the block to lubricate all moving parts, and coolant channels keep the engine from overheating.

The 350 block was first produced by Chevrolet in 1967 and remained in production for decades. It became one of the most common V8 blocks in American vehicles because it was affordable to manufacture, reliable, and straightforward to modify. You will find 350 blocks in Chevrolet cars, trucks, and performance vehicles from the late 1960s through the early 2000s, and they are still used in custom builds and engine swaps today.

Key Takeaways

  • The 350 block is a V8 casting with eight cylinders that holds the pistons, crankshaft, and main bearings.
  • Chevrolet made 350 blocks from 1967 onward, and they appear in thousands of vehicles across multiple decades.
  • The block material is either cast iron (heavier, more durable) or aluminum (lighter, runs hotter), depending on the year and process.
  • A 350 block can be identified by casting numbers stamped on the block itself, which tell you the year and original vehicle it came from.
  • Common problems include cracking, corrosion, and bearing wear, all of which can be repaired or managed depending on the severity.

Cast Iron versus Aluminum 350 blocks

Most 350 blocks are cast iron, which is heavier but stronger and more resistant to heat stress. Cast iron blocks can withstand higher boost pressures and more aggressive tuning without cracking. They also hold oil better and require less maintenance of the cooling system.

Some later 350 blocks, particularly those used in trucks and performance applications, were cast from aluminum. Aluminum blocks are roughly 40 percent lighter than iron, which improves acceleration and fuel economy. However, aluminum conducts heat faster, so the engine runs hotter and requires a more efficient cooling system. Aluminum is also softer and more prone to cracking under extreme stress, and the cylinder walls wear faster without proper maintenance.

If you are rebuilding or swapping a 350 engine, the choice between iron and aluminum affects your cooling setup, tuning limits, and long-term durability. Iron is the safer choice for high-horsepower builds; aluminum is better if weight savings matter more than maximum power.

How to identify a 350 block by casting number

Every 350 block has a casting number stamped into the iron or aluminum. This number tells you the year the block was cast and which Chevrolet vehicle it originally came from. The casting number is usually found on the right (passenger) side of the block, near the oil filter or on the back of the block near the bellhousing.

The casting number is not the same as the engine serial number. It is a code like "14010015" or "3970010" that Chevrolet used to track production. You can cross-reference this number with a 350 casting number chart to learn the casting date and original process. This information matters if you are buying a used block, because it tells you whether the block came from a truck, a car, or a performance engine — and whether it has been rebuilt or modified before.

If you cannot find the casting number or it is worn away, you can still identify the block by its external features: the number and location of bolt holes, the size of the main bearing caps, and the shape of the oil pan mounting surface. A machine shop or experienced engine builder can usually identify a 350 block by sight.

Common 350 block problems and repairs

Cast iron 350 blocks are durable, but they can develop cracks over time, especially if the engine has overheated or been subjected to extreme cold. Cracks usually appear around the cylinders or near the main bearing saddles. Small surface cracks can sometimes be sealed with epoxy or metal-bonding compounds, but deep cracks that go through the cylinder wall or main bearing area usually require the block to be replaced or sent to a machine shop for welding and re-boring.

Corrosion is another common issue, particularly in blocks that have sat unused or been exposed to moisture. Rust inside the cooling passages can restrict coolant flow and cause overheating. Rust in the oil passages reduces lubrication. If corrosion is light, the block can be flushed and treated with a rust converter. If it is severe, the block may need to be boiled out or chemically cleaned by a machine shop.

Bearing wear happens when the crankshaft spins on the main bearings for hundreds of thousands of miles. You will notice this as a knocking sound from the engine, especially when you accelerate. Worn bearings can be replaced without removing the block from the vehicle, but the crankshaft must be inspected for scoring. If the crankshaft is damaged, it must be ground down to the next undersize, and new bearings of the matching undersize must be installed.

Rebuilding versus replacing a 350 block

If your 350 block is cracked, severely corroded, or has bearing damage that cannot be repaired, you have two choices: rebuild the block or replace it with a used or remanufactured block.

Rebuilding means disassembling the engine, cleaning the block, repairing or replacing damaged parts, and reassembling everything. A full rebuild includes new pistons, rings, bearings, gaskets, and seals. The block itself is bored and honed to accept new pistons. A machine shop will charge between $1,500 and $3,500 for a basic rebuild, depending on the extent of the damage and the shop's labor rates. A performance rebuild with upgraded pistons and a stroker crankshaft can cost significantly more.

Replacing the block means sourcing a used 350 block from a salvage yard or buying a remanufactured block from an engine supplier. A used block typically costs $300 to $800, depending on condition and mileage. A remanufactured block comes fully rebuilt and tested, and costs $1,200 to $2,500. Replacement is faster than rebuilding if the block is severely damaged, but you are taking a chance on the condition of a used block unless you have it inspected before purchase.

350 blocks in engine swaps and custom builds

The 350 block is popular in engine swaps because it is compact, affordable, and compatible with many transmission and mounting options. A 350 block can be installed in older Chevrolet vehicles, trucks, and even non-Chevrolet cars with custom engine mounts and exhaust work. The block itself is the same whether it came from a 1970 Chevelle or a 1995 Suburban, so sourcing parts and finding technical information is straightforward.

In custom builds, a 350 block can be bored and stroked to increase displacement, fitted with high-compression pistons, and topped with performance cylinder heads and an aggressive camshaft. A mildly modified 350 produces 350 to 400 horsepower; a heavily modified one can exceed 500 horsepower. The block's strength and simplicity make it a good foundation for these builds, though aluminum blocks are less suitable for extreme modifications.

Frequently Asked Questions

What is the difference between a 350 block and a 327 or 400 block?

The 350, 327, and 400 are all Chevrolet V8 blocks, but they differ in bore and stroke — the diameter of the cylinders and the distance the piston travels. A 350 has a 4-inch bore and 3.48-inch stroke. A 327 has a smaller bore (4 inches) and shorter stroke (3.25 inches), making it lighter and better for high-RPM engines. A 400 has a larger bore (4.125 inches) and longer stroke (3.75 inches), making it heavier and better for low-end torque. The blocks look similar, but they are not interchangeable.

Can I use a 350 block from a truck in a car engine?

Yes. A 350 block is a 350 block regardless of whether it came from a truck or a car. The internal structure is the same. The only differences may be in the external mounting points for accessories like the alternator or power steering pump, which can be adapted with different brackets. A truck block is often a good value because truck engines are less sought after by enthusiasts.

How do I know if my 350 block is cracked?

Small cracks may not show symptoms until they grow. Look for white crusty deposits around the block (coolant seeping out), oil in the coolant or coolant in the oil (visible on the dipstick), or a sweet smell from the exhaust (coolant burning). If you suspect a crack, a machine shop can perform a pressure test or dye penetrant test to confirm it. Do not ignore these signs — a cracked block will eventually fail completely.

What does it cost to have a 350 block bored and stroked?

Boring and stroking a 350 block requires machine work, new pistons, a new crankshaft, and new connecting rods. The machine shop work alone (boring, honing, and line-honing) costs $400 to $800. New internal parts cost $600 to $1,500 depending on quality. Labor to assemble the engine is another $800 to $1,500. A complete stroker build typically costs $2,000 to $4,000 in parts and labor, not including cylinder heads, intake, or exhaust.

Is a 350 block better than a modern engine for a swap?

A 350 is simpler, cheaper, and easier to find parts for than many modern engines. It is also easier to modify and tune. However, modern engines are more fuel-efficient, produce more horsepower per cubic inch, and require less maintenance. The choice depends on your goals — a 350 is better if you want classic looks and straightforward customization; a modern engine is better if you want reliability and efficiency.