Difference Between Chevy 350 and 400 Small Block

Photo by Kenny Eliason on Unsplash

Planetwagon is reader-supported. When you buy through links on our site, we may earn an affiliate commission.

In the heyday of muscle car fervor, GM sought to establish its dominance with the Camaro, necessitating the birth of iconic small-block engines. The Chevy 350 and 400 emerged as pivotal players in this era, each carving a unique niche within the revered Small Block family.

The differences between them may seem minuscule, but their characteristics can be strikingly different depending on how they’re built. From their displacement to their bore size to their compression ratio, these two engines can provide an entirely unique experience behind the wheel.

In this article, we’ll explore the difference between Chevy 350 and 400 small blocks to help you decide which is best for your ride.


Overview Of The Chevy 350 Small Block

The Chevy 350, or the 350 Small Block, emerged in 1967 to meet the demand for high-performance engines, initially debuting in the Chevy Camaro. With 295-300 hp and 380 lb/ft of torque, the 5.7L 350 cubic inch L-48 small block became a powerhouse.

Boasting a 10.25:1 compression ratio, it accelerated the Camaro from 0 to 60 mph in 7.6 seconds, rivaling the 67 Mustang GT.

The 350 quickly expanded its reach, becoming an option for various Chevy models and finding applications in passenger cars, sports cars, and trucks.

Production continued until 2003, succeeded by the Generation III LS in 1997, but the 350 remains popular among classic car restorers and hot rodders.


The 400 Small Block was introduced in 1970 for bigger Chevy vehicles. It became a dependable engine known for low-end torque.

The 400 Small Block engine was used in Impala, Chevelle, and Caprice cars, as well as GMC trucks and SUVs. It had an initial horsepower of 265 with a 2-barrel carburetor, and a 4-barrel option was added in 1974.

The 400 Small Block, with its limited production run until 1980, has become an absolute legend in the racing world. And boy, does it know how to shine in off-road scenarios with its beastly torque capabilities!


What Are the Differences Between The Chevy 350 and 400?

While both engines share similar engineering and construction, their primary areas of focus differ significantly. In this section, we’ll explore how the two engines differ from one another.

Difference #1 – Horsepower Generated

The small block 350 had around 295 to 300 horsepower during its first generation, but these numbers could vary depending on the configuration.

In contrast, the 400 small blocks had horsepower ratings of around 265, depending on the specific configuration and carburetor.

While neither engine could boast monstrous horsepower, the 350 stood out as a high-performance option. This distinction is evident in its application in classic vehicles like the Corvette and Camaro.

Difference #2 – The Bore and Stroke Are Different

The Chevy 350 and 400 small blocks have different bore and stroke dimensions, showing GM’s distinct engineering choices.

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

The bigger bore size in the 400 small blocks made GM use a Siamese design that removed channels for water and coolant circulation between the cylinders.

The larger cylinders increase power but also cause problems like overheating and blown gaskets. GM tried to fix this with “steam” holes, but it wasn’t completely successful.

The 400 small block engines had weaker cylinder walls due to the Siamese design and larger bore, resulting in overheating issues linked to radiator leaks and faulty water pumps.

Consequently, restorers often add extra cooling system features for optimal performance of their 400 small block engines.


The 400 small block stands out due to its unique Siamese cylinder configuration, where the cylinder walls are interconnected without intervening coolant passages.

This design, aimed at accommodating a larger bore, introduces a potential hurdle: overheating challenges, especially under intense conditions like high-performance or high-load scenarios. The lack of separate coolant passages necessitates careful cooling management strategies.

On the flip side, the Chevy 350 adopts a more conventional cooling system. Its cylinders boast separate coolant passages, enhancing overall cooling efficiency. This design facilitates better heat dissipation and aids in maintaining optimal engine temperatures across diverse operational circumstances.

The 350’s approach of individual coolant passages contributes to robust cooling performance, making it a reliable choice, particularly in scenarios where efficient heat management is critical.

Difference #3 – The Main Journals and Crankshaft

The 350 boasts 2.45-inch main journals, while the 400 Small Block (SBC) takes a step further with larger 2.65-inch diameter journals. This variation extends to the main caps, with the 400 featuring more comprehensive caps that aren’t interchangeable with the 350.

Notably, the crankshaft configurations diverge between the two. The 400 employs an externally balanced crankshaft, complemented by a harmonic balancer.

In contrast, the 350 opts for internal balancing. This nuanced distinction in balancing methods contributes to the engines’ overall performance characteristics.

Another key factor to consider is the main bolt setup. The ’70 – ’72 small block 400 was equipped with four-bolt mains, enhancing its structural robustness.

However, in subsequent production years from 1973 to 1979, the 400 transitioned to two-bolt mains. This change reflects the evolving design choices made by Chevy during different production periods.

Difference #4 – Casting Numbers

When it comes to telling apart the Chevy 350 and 400 engines, you need to pay attention to something called casting numbers. These are like ID codes stamped on the engine block or head that help you choose the right parts when working on your engine.

To find these numbers, look at the back of the engine block near the transmission. A bit of degreaser and a wire brush will help you clean things up and read the numbers clearly.

For the Chevy 400 engine, there are three main casting numbers: 330817, 3951509, and 3951511. Here’s the cool part – the 1511 series usually has four-bolt mains, which makes the engine structure stronger. On the flip side, the 0817 and 1509 casting numbers more often come with two-bolt mains.

Now, let’s talk about the webbing. In the two-bolt mains (0817 and 1509), there’s more nickel in the webbing compared to the four-bolt mains. This extra nickel makes the 400 block tougher than the Chevy 350.

Difference #5 – Cost

At first glance, the 350 small block appears as a more budget-friendly option, typically costing around $2,000 less than its 400 counterpart. However, this apparent cost advantage comes with nuances that savvy buyers should consider.

When scouting for the best deal online, it’s not merely about securing the lowest price tag but also ensuring that the purchase includes a warranty.

A warranty becomes a crucial safeguard, preventing potential financial pitfalls associated with unforeseen issues that may arise with the engine.

The intricacies of pricing extend beyond the initial purchase. The 350 small block, with its extensive production history and widespread use, enjoys a robust market for aftermarket parts. This abundance not only makes modifications more accessible but also contributes to the overall affordability of the 350.

On the flip side, the 400 small block, with its shorter production span, poses challenges in finding certain components, potentially impacting the cost and availability of replacement parts.

Difference #6 – Displacement

The Chevy 400 small block boasts a larger displacement of 400 cubic inches (6.6 liters), overshadowing the 350’s 350 cubic inches (5.7 liters). This disparity in size translates directly to variations in power and torque output.

With its substantial 400 cubic inches, the 400 small block is engineered to deliver heightened performance, making it an optimal choice for endeavors demanding increased power and torque.

Applications like racing or heavy-duty towing benefit significantly from the additional displacement, providing a robust and reliable performance.

Contrastingly, the Chevy 350 strikes a balance between power and efficiency, with its 350 cubic inches catering to a diverse range of applications.


What Are The Similarities Between Chevy 350 and 400?

When exploring the common ground between the Chevy 350 and 400 engines, it becomes apparent that these powerhouses share several fundamental characteristics. 

90-Degree V-Shaped Design

Both the Chevy 350 and 400 engines boast a 90-degree V-shaped configuration. This design choice contributes to their overall efficiency and performance, aligning with the classic V8 engine layout that’s been a hallmark of Chevy’s small block engines.

Cast Iron Blocks and Cylinder Heads

A shared trait between the two engines is their construction using cast iron blocks and cylinder heads. 

Similar Dimensions and Weight

Both engines align closely, sharing approximate heights, widths, and lengths. Both engines tip the scales at around 200 lbs, adding a layer of interchangeability. This similarity in size opens the door to the possibility of performing a motor swap between the Chevy 350 and 400 if one desires a change.

Eight Cylinders with Two Valves Each

A defining feature common to both engines is their eight-cylinder arrangement, with each cylinder housing two valves. This configuration contributes to the overall power output and efficiency, showcasing the shared design philosophy that underpins these small block engines.


Conclusion – Which Is The Better Motor Between Chevy 350 vs. 400 Small Block?

The dispute over the supremacy between the Chevy 350 and 400 small block engines is the stuff of heated discussions. Opinions, much like the exhaust notes of these iconic engines, vary across forums dedicated to these powerhouses. Yet, when the rubber meets the road, the consensus leans towards the 350. Why? It’s all about power and reliability.

The 350 small block has earned its stripes as the go-to choice for many restoration enthusiasts. The availability of parts, coupled with a robust market for aftermarket blocks, makes it the pragmatic option.

When you’re knee-deep in a restoration project, the last thing you want is to be hunting down elusive components or facing compatibility issues.

The 350’s ubiquity ensures a smoother ride through the restoration journey. It’s a power-packed, reliable workhorse that has stood the test of time, earning the trust of those who turn wrenches in the pursuit of automotive perfection.



Please enter your comment!
Please enter your name here