Key Takeaways

  • The 400 small block has a larger bore than the 350.
  • The first 350 small block engines competed with other competitors' big block engines.  
  • The performance of the 350 small block motor makes it the more reliable of the two.
  • The 400 had Siamese cylinders, which created potential overheating problems.

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Have you ever wondered what the difference was between the Chevy 400 small block and the 350? Let’s dig into each and see what makes these motors unique.

The 350 (5.7L) L-48 small block engine debuted in 1967 as a high-performance engine for the new Camaro. The engine produced 295 hp. The 400 (6.6L) was introduced in 1970 and was used in full-sized models like Chevelles, Caprices, and Impalas. It produced 265 hp with a 2 bbl carburetor.

One of the areas that many classic car restorers need clarification on is the difference between the 400 small blocks and 350. While both these small block engines have their advantages, there are some key differences, and depending on what you want to achieve in your build, it is essential to know what is what. Let’s dive into these two small block engines to see what General Motors had in mind when it produced them. But first, some history.

Table of Contents

What Is The History of the 350 Small Block Vs. the 400?

During the late sixties, GM was heavy in the throws of muscle car mania. The Impala and Chevelle dominated the Big Block scene with their 396s and 402s (not to mention the Corvette with a 7.0 L 427 cubic inch Mark IV engine). GM needed a small block engine that it could offer in a new sports car it was manufacturing called the Camaro.

The 350 Small Block

GM needed a high-performance engine option for the new ‘67 Chevy Camaro, so they turned to the 5.7L 350 cubic inch L-48 small block. The engine produced about 295 - 300 hp and 380 lb/ft of torque. The engine had a 10.25:1 compression ratio, which was enough to blister the new sports car down the track with a 0-60 mph time of 7.6 seconds. (The time is within 3/10ths of a second of the 67 Mustang GT). A year later, the same engine made its way into the Chevrolet Nova, and it wasn’t long before the 350 V8 or a variant popped up as an option for most of the Chevy lineup.

Over the next decade and a half, several variants of the 350 emerged and were used as options in almost every passenger car, sports car, and truck that GM or its divisions made. The 350 was manufactured until late 2003 when it had been superseded by the Generation III LS in 1997. The 350 is still produced as a crate engine in various forms and is a favorite among classic car restorers and hot rodders.

The 400 Small Block

The 400 Chevy small block (6.6 L) didn’t have the legacy the 350 enjoyed. It was introduced in 1970 as an engine option for full-sized Impalas, Chevelles, and Caprices and was produced for a decade. During that time, the 400 saw extensive use in full-sized passenger cars, GMC trucks, and SUVs. The initial offering in 1970 made 265 hp due to the engine being mated to a 2bbl carburetor. (Although a 4bbl option was available for the 1974 engine).

The 400 was simply not designed to be a high-performance engine. Instead, GM wanted a workhorse of an engine that could produce low-end torque (which made it perfect for pickup trucks and SUVs). While the 350 might have more power, the 400 small block was more efficient for towing, hill climbing, and consistent low-end power. While neither V8 engine was very fuel efficient, the 350 was probably the better of the two due to the lower displacement.

The 400 small block was produced for most vehicles through 1980, and due to the number of vehicles it appeared in, it is a popular choice for racing. Today, the 400 small blocks are easily adapted to off-road racers where road conditions are rougher, and the need for high torque capabilities is greater.

What Are the Differences Between the 400 vs the 350?

There are some commonalities between the two engines, such as both are 90-degree V-shaped engines with cast iron blocks and cylinder heads. (Although the engines have the same block design, the 400 has steam holes to vent heat from the cylinders).

The engines are roughly the exact dimensions in height, width, and length. Both engines weigh about the same (around 200 lbs) and have eight cylinders with two valves in each chamber. (Technically, you could perform a motor swap if you wished to).

Yet, as much as they might have in common, there are several key differences between the 400 and the 350 factory blocks.

The Horsepower They Generated

The most obvious difference is in the power that these two engines generated. Depending on the variant of the small block 350, the horsepower could be 295 - 300 hp for the first Generation. The compression started at 10.25:1 but was soon carved back when emissions regulations began to take hold.

The 400 small blocks had horsepower ratings ranging between 265 and 265 depending on the configuration and the carb attached. While neither engine produced monstrous horsepower, the 350 was a high-performance enough engine to be used in classic vehicles like the Corvette and Camaro.

The Bore and Stroke Are Different

The 400 small block has a bore dimension of 4.18 and a stroke of 3.75 with 5.56-inch connecting rods. The 350 has a smaller bore opening of 4 inches, a stroke of 3.48 inches, and 5.7 longer connecting shafts.

The increased bore size on the 400 small blocks meant that GM had to siamese the cylinders together and eliminate any channels for circulating water and coolant. The advantage of this configuration is that you achieve more power through the bored-out cylinders, but the disadvantage is that overheating and blown gaskets were a definite possibility. GM tried to correct this issue by putting “steam” holes in the block and heads, but they were only moderately successful. Owners often complained about overheating issues. (In fairness, the 350 SBC had some overheating issues, primarily to the radiator tending to leak or faulty water pumps). Due to the Siamese design and the additional bore size, the cylinder walls were not as strong on the 400 small block engines as on other Chevy small blocks. Many restorers must add lines to the cooling system to help keep their 400 small blocks running effectively.

The Main Journals

The 350 had 2.45-inch main journals as opposed to the 400 SBC, which had 2.65-inch diameter journals. The main caps on the 400 are more comprehensive and are not interchangeable with the 350. The crankshaft was externally balanced with a harmonic balancer on the 400, whereas the 350 was internally balanced.

The ‘70 - 72 small block 400 was made in four-bolt mains, while the engine had two-bolt mains in its later runs from 1973 to 1979.


A 350 small block costs about $2k cheaper than the 400. While it is always wise to search for the best price online, ensure that you are purchasing an engine with a warranty not to waste your money.

Generally speaking, modifications on a 350 small block are more manageable due to the availability of aftermarket parts. Since the 400 small blocks were not made for as long, some components are becoming increasingly more challenging to find.

What Is The List of Differences Between 400 Small Block vs. 350?

Below we have provided the difference between the Chevy 350 and 400 small block engines.

Item 5.7 L 350 V8 Small Block 6.6 L 400 Small Block
Production 1967 - 2002 1970 - 1980
First Car Used 1967 Camaro 1970 Impala, Chevelle
Engine Capacity 5.7 L 6.6 L
Horsepower 295 hp 265 hp
Torque 385 lb/ft 325 lb/ft
Bore 4.0 inches 4.18 inches
Stroke 3.48 inches 3.75 inches
Connecting Rod Length 5.7 inches 5.56 inches
Main Journals 2.45 inches 2.65 inches
Balance internal External
Chamber Configuration Standard Siamese
Block Cast iron Cast iron
Cylinder Heads Cast iron Cast iron
Weight 195 lbs 200 lbs
Cylinder Walls Stronger Weaker

Which Is The Better Motor?

Most restorers believe that the 350 small block is the more reliable of the engines when compared head to head. While there are lots of threads extolling both engines on the forum community dedicated to both, the significant difference is in power and reliability. Since parts are more readily available (as are aftermarket blocks), the 350 small block is usually the way to go.

The Chevy 400 Small Block VS 350 (List Of Differences)

About The Author

Charles Redding

Charles Redding

I've spent many years selling cars, working with auto detailers, mechanics, dealership service teams, quoting and researching car insurance, modding my own cars, and much more.

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