It’s an engine-building debate that spans generations: cast vs. forged. If you have ever spent time walking around a Saturday classic car show, you’ve heard these terms thrown around when car guys talk about the crank, rods, and pistons in the bottom end of their engines or future engine builds they’re planning.

Some suggest going with forged. Best is best, right? But in the grand scheme of engine building, going for pricier items like a forged crank and forged pistons might be overkill depending on your build and budget. So when can you afford to save a few bucks with cast parts and when do you actually need to drop the extra coin on the tough stuff?

Cast Crankshafts

Cast crankshafts are produced using a process known as sand or die casting, in which molten metal, usually iron or steel, is poured into a pre-shaped mold and allowed to cool into its final form. This approach is rooted in efficiency and volume production. Once solidified, the resulting raw casting requires only minor machining to achieve the final dimensions and surface finishes needed for engine assembly.

The key advantage of cast crankshafts lies in their manufacturing economics. Casting allows for low-cost, high-volume production, with minimal investment in tooling and setup compared to more labor and time-intensive processes like forging. Because the shape of the crank is formed directly in the mold, the amount of post-processing, such as machining and heat treating, is significantly reduced.

The SCAT forged crankshafts seen here are ready to be machined.

While they may not offer the same fatigue resistance or tensile strength as a forged crank in the cast vs forged debate, a well-designed cast crankshaft can easily handle the demands of most naturally aspirated engines. For instance, SCAT’s 9000 Series cast steel crankshafts are recommended for power levels below 500-550 horsepower and a max rpm of 6,000-6,500.

Stepping Up To Forged

Unlike their cast counterparts, forged crankshafts are formed through a high-pressure deformation process that aligns and strengthens the metal at the molecular level. The process begins with a chunk of hot-rolled steel, typically heated to temperatures between 1,800-2,100 degrees Fahrenheit, that is then placed between two heavy-duty dies shaped to approximate the geometry of a crankshaft. Massive hydraulic or mechanical forging presses, often rated in the thousands of tons, force the metal to conform to the die shape under immense pressure.

Some forged crankshafts are forged into a rough blank and then finish machined, other are machined directly from a forged steel bar stock like this.

The result is a crankshaft blank that retains a grain structure that closely follows the contours of the crank throws and journals. This grain flow significantly enhances mechanical properties such as tensile strength, impact resistance, and fatigue life, making forged crankshafts ideal for applications that will be utilizing a power adder or high-RPM applications.

Most aftermarket forged crankshafts for small-block Chevy and big-block Chevy applications are made from 4340 steel. While you can use one of these crankshafts in a lower-performance engine without issue, they are best reserved for small-block builds looking to make upwards of 1,000 horsepower with a power adder or big-blocks churning out up to 1,500 horsepower.

Crankshaft strength isn’t simply about surviving a single high-load pull. OEM crankshafts are engineered with durability in mind, often expected to endure well over 100,000 miles of use. That kind of lifespan depends on more than just tensile strength or elongation; it involves fatigue resistance, material stability, and proper load distribution over time. This is why when some suggest a stock crank can handle the same high-horsepower as a forged crankshaft, it’s important to remember how long that crank will last at that power level.

H-Beam Connecting Rods

All factory OEM connecting rods that came in small-block and big-block Chevys were forged, usually out of 1045 or 5140 steel. Even the commonly misunderstood powdered metal rods GM used in the 1990s small-blocks and Gen II LT1s are forged. The factory just started the forging process with steel in powdered form instead of a solid block of metal. So, instead of discussing cast vs forged rods, we will discuss H-beam vs I-beam rods.

H-beam connecting rods have long been regarded as the go-to option for applications demanding exceptional strength and reliability under extreme load. Their distinctive “H”-shaped cross-section offers superior rigidity, making them particularly well-suited for forced induction engines, where elevated cylinder pressures are the norm. As a result, H-beams are commonly found in high-horsepower builds in drag racing platforms or engines running significant boost, nitrous oxide, or similar power adders.

H-beam rods have long been regarded as the go-to option for engine builds requiring a connecting rod that can handle high cylinder pressures from power adders.

One of the standout advantages of the H-beam design is its ability to resist lateral bending and abnormal loading forces. This structural integrity helps prevent rod deformation under uneven combustion or detonation scenarios. However, this increased strength often comes with a weight penalty: H-beam rods are typically a little heavier than their I-beam counterparts. While the weight difference might seem minor, it can be a critical factor in high-RPM or motorsport applications where rotating mass significantly impacts engine response and acceleration.

Due to their mass and stiffness, H-beam rods are less commonly used in naturally aspirated, high-revving engines. They don’t handle tensile (stretching) loads as well as I-beams and may introduce limitations in engines that routinely operate at elevated RPMs.

I-Beam Connecting Rods

Though both H-beam and I-beam rods serve the same mechanical function, their designs are optimized for different operating stresses. I-beam rods excel in handling tensile forces, which makes them better suited for high-revving naturally aspirated engines where stretching loads dominate. Their thinner profile and streamlined cross-section are ideal for reducing overall mass in the rotating assembly.

I-beams are generally lighter than H-beams, which provides two distinct benefits: improved engine responsiveness and reduced stress on other internal components. This makes them a preferred choice in performance builds where throttle response and high-RPM durability are prioritized over brute strength.

All stock small-block and big-block connecting rods are forged I-beams, but aftermarket I-beam rods can be found with better designs and materials for higher horsepower and RPM capability.

Structurally, I-beam rods are more effective at managing normal combustion loads without deflection, giving them solid resistance to side-loading or flex during rapid engine cycling. Their compact dimensions can also be advantageous in engines with tight packaging constraints or specific geometry requirements.

While they may not offer the same brute resistance to extreme cylinder pressure as an H-beam, I-beam rods strike an optimal balance between weight, size, and high-speed performance, making them a top pick in road racing, autocross, or naturally aspirated street/track builds. Stock small-block I-beams are tough, but it is recommended to step up to a 4340 I-beam rod for engine builds making 500-700 horsepower, and H-beam rods when you step up to a power adder looking to make more than 700 horsepower.

Cast Pistons For Entry Level

Cast pistons are manufactured by pouring molten aluminum alloy into a mold, where it solidifies into a near-net shape that closely resembles the final piston form. Similar to the casting process used for crankshafts, this method minimizes the amount of machining required, making it highly cost-effective and well-suited for mass production. For decades, casting has been the standard approach for OEM piston manufacturing, offering a reliable balance of performance, consistency, and economy.

OEM cast pistons are perfectly fine for stock or very mild naturally aspirated performance applications.

Although advancements in material science have led many modern applications to adopt hypereutectic aluminum alloys for improved thermal and wear characteristics, traditional cast pistons remain in use for lower-stress engines and cost-sensitive builds. Their simplicity, proven durability in standard operating conditions, and ease of production continue to make them a viable solution in many factory and budget-conscious performance applications.

Upping The Silicon Content

All cast aluminum pistons include a certain percentage of silicon, typically in the range of 10-12 percent. At this ratio, the silicon and aluminum form a balanced alloy with good strength, wear resistance, and thermal stability. However, by increasing the silicon content beyond this point, manufacturers can create what are known as hypereutectic pistons.

SCAT rotating assemblies have a choice of hypereutectic or forged pistons. The Keith Black hypereutectic pistons offered are a step up from stock cast pistons.

Hypereutectic pistons typically contain 16-18 percent silicon, a modification that significantly improves several key characteristics while still utilizing the cost-effective casting process. The elevated silicon content increases hardness and reduces thermal expansion, which allows for tighter piston-to-wall clearances. This results in improved combustion efficiency, reduced oil consumption, and greater resistance to scuffing under elevated temperatures. These traits are especially beneficial in modern OEM high-output, naturally aspirated, or mild forced-induction engines.

Despite these advantages, hypereutectic pistons are not without limitations. While stronger than conventional cast pistons, their increased silicon content also makes them more brittle and prone to cracking under extreme detonation or the high cylinder pressures found in aggressive boost or nitrous setups. As power levels climb and operating conditions become more severe, the structural demands exceed what a cast-based alloy can handle. While these have proven themselves to handle 400 to 600 horsepower in small-block builds, the cast vs forged conversation will lead you to forged pistons for serious performance builds that need the extra durability.

A fresh shipment of aluminum bar-stock delivered to Wiseco to make pistons.

4032 And 2618 Forged Slugs

Forged pistons begin their life as heated billets of aluminum alloy, which are placed into precision dies and formed under immense pressure, often tens of thousands of psi in the same way forged cranks are forged. This high-pressure deformation aligns the grain structure of the metal, significantly increasing material density and ductility compared to cast and hypereutectic pistons.

The bar stock is cut into pucks before being heated and forged.

The result is a stronger, more resilient piston blank capable of withstanding extreme combustion forces. However, this process also requires more extensive post-forging machining to achieve final dimensions and features, which contributes to the higher cost of forged pistons. Forged pistons are typically produced using one of two aluminum alloys: 4032 or 2618, each offering distinct performance characteristics suited for different levels of engine stress.

the blank piston pucks are heated and then pressed into a mold using tens of thousands of pounds of hydraulic pressure.

4032 alloy contains approximately 10–12% silicon, similar to many hypereutectic cast pistons, which helps reduce thermal expansion and allows for tighter piston-to-wall clearances. These tighter tolerances minimize cold-start noise, reduce long-term wear, and contribute to improved engine longevity. As such, 4032 forged pistons are a great balance for high-performance street engines that are looking to run forced induction or nitrous and not suffer the cons of 2618 forgings.

For maximum power and the most demanding conditions, 2618 alloy is the racing industry’s go-to material. Containing less than 1-percent silicon, 2618 provides significantly greater malleability and impact resistance, allowing it to withstand extreme pressures, high RPM, large nitrous loads, and high-boost levels. Its tensile strength is notably higher than 4032 making it the preferred choice for all-out race engines or high-horsepower forced-induction builds looking to creep toward four-digit horsepower.

Beginning, middle, and final product of a Wiseco forged piston.

However, this performance comes with trade-offs. Due to its low silicon content, 2618 expands more as it heats up, requiring greater piston-to-wall clearance. This means increased piston noise at cold start and more oil consumption during warm-up, but those are small compromises for a material capable of surviving the harshest environments inside a combustion chamber.

This SCAT rotating assembly for a 383-stroker small-block Chevy consists of a cast steel crankshaft, I-beam rods, and Keith Black hypereutectic pistons. For a street small-block looking to make under 500 horsepower with a 6,000rpm redline, this is the perfect fit.

A Budget Based On Needs

While it is possible to build a 500-horsepower 383 small-block or 496 big-block using a 4340-forged crank, H-beam rods, and 2618-forged pistons, you could achieve a cheaper and more streetable build using a cast crank, I-beam rods, and hypereutectic pistons that will last the life of your project for far less. On the flip side of the cast vs forged debate, it would be foolish to think that cast internals could handle a 1,000-horsepower twin-turbo build for more than one dyno pull, costing you more in the long run compared to building it right the first time.