What Is A 4 Bolt Main?

Are you curious to know what is a 4 bolt main? You have come to the right place as I am going to tell you everything about a 4 bolt main in a very simple explanation. Without further discussion let’s begin to know what is a 4 bolt main?

What Is A 4 Bolt Main?

In the realm of automotive engineering, the term “4-bolt main” often surfaces in discussions about engine strength and durability. As a crucial component within the heart of an engine, the 4-bolt main configuration plays a pivotal role in supporting the engine’s power and reliability. Let’s delve into the significance of the 4-bolt main, its role in engine construction, and its impact on performance.

Foundation Of Engine Strength:

The term “4-bolt main” refers to a specific design feature within an engine block, particularly in relation to the main bearing caps. These caps are crucial components that secure the crankshaft in place within the engine block.

Key Components Explained:

  • Main Bearings: The main bearings are the bearings within the engine block that support the crankshaft, allowing it to rotate smoothly. These bearings are positioned along the crankshaft’s main journals.
  • Main Bearing Caps: These are sturdy metal caps that cover and secure the main bearings, holding the crankshaft in place and maintaining its alignment within the engine block.

Significance Of 4-Bolt Main:

The designation of “4-bolt main” signifies that the main bearing caps are secured to the engine block with four bolts per cap. This configuration provides enhanced stability and strength to the crankshaft, reducing the risk of movement or flexing during high-stress situations, such as high RPMs or increased power output.

Strength And Durability:

Engines with a 4-bolt main configuration are often favored for their increased strength and durability, particularly in high-performance applications where the engine is subjected to significant stresses. The additional bolts distribute the forces exerted on the crankshaft more evenly, reducing the likelihood of distortion or failure.

Performance Impact:

While the 4-bolt main configuration contributes to the engine’s overall strength, it’s important to note that the number of main bolts is just one aspect influencing an engine’s performance. Factors such as material quality, machining precision, and overall design also play pivotal roles in determining an engine’s reliability and performance.

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Evolution And Variations:

Not all engines utilize a 4-bolt main configuration. Some engines may employ a 2-bolt or 3-bolt main design, which can still offer reliability and adequate strength for certain applications. Additionally, advancements in materials and engineering have led to innovations that enhance engine strength without relying solely on the number of main bolts.


In the intricate world of engine construction, the 4-bolt main configuration stands as a testament to the pursuit of durability and strength. Its design, with four bolts securing the main bearing caps, reinforces the engine’s foundation, providing stability and resilience, particularly in high-performance scenarios. While just one element in a complex system, the 4-bolt main remains a hallmark of engine design, contributing to the power and reliability that automotive enthusiasts cherish.


What Is The Difference Between A 4 Bolt Main And A 2 Bolt Main?

Any time you increase horsepower, torque and cylinder pressure, you increase crankshaft load. It would take quite a bit more stress to rip-out 4 bolts than it would just 2, so that’s why the 4 bolt mains are stronger than the 2 bolt mains. This is the theory behind it anyway.

How Do You Tell If A 454 Is A 4 Bolt Main?

One way to tell is look above the oil filter boss.. all the early 4 bolt blocks were drilled and tapped for an external oil cooler, if the block has two pipe plugs (one 1/2″ and one 1/4′) its a 4 bolt.

How Much Hp Can A 4 Bolt Main 350 Handle?

The iron 4 bolt main will handle 600 hp on a factory block. A two bolt main iron factory block that’s got a splayed 4bolt and half hard block will handle 700hp these are in naturally aspirated form.

Is A 5.7 Vortec A 4 Bolt Main?

The 2 bolt main 5.7 vortec’s were put in the 1500 and 2500 LT. duty truck’s. The 4 bolt main 5.7 vortec’s were put in the 2500 HD and 3500.

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