The Benefits of Forged Pistons

February 22, 2012

A look at how forged pistons are made, their unique properties, and their advantages over traditional cast pistons.

Forged Pistons

The use of forged pistons by racing tuners and mechanics is evidence of this particular piston's capability. The difference between a normal or cast piston and a forged piston is the manufacturing technique. Traditional cast pistons are considered good enough by most engine tuners and builders when it comes to stock setups, and suffer no drawback in terms of compression and service life. The cast piston is most common on all mass-produced engines, because the casting process of making this type of piston presents a low cost opportunity to the manufacturer.

Manufacturing Techniques
Cast pistons are made with the use of large, specialized equipment made up of a mold where the mixture of aluminum, alloys and silicone are poured to create the piston's shape. Forged pistons employ a single lump of billet alloy which is stamped by the use of a die. The shape of the die determines the size and shape of the piston.

Forged Pistons
Performance enthusiasts and custom engine builders prefer the use of forged pistons because they are more durable and easily customized to any configuration, which is essential in engine tuning. Some engine applications may require a flycut on the piston crown to assist in valve relief, and this can be easily achieved using a forged piston. The manufacturing techniques employed in the making of a forged piston make it stronger, as there is more surface area concentrated onto its shape.

Forged pistons are also easy to manufacture as there is no need for big, heavy and expensive casting equipment as employed in the manufacture of cast pistons. This does not necessarily mean that forged pistons are better than cast pistons. In fact, the technology used in the making of cast pistons is state of the art compared to the method of forging alloys. The difference actually lies in application.

The main characteristic that makes forged pistons excel in high performance applications is strength and durability. The high silicon content of cast pistons makes them brittle compared to forged pistons. Silicon gives the metal lubricity and is mixed in the alloy to limit heat expansion. This is primarily the reason why cast pistons require careful handling. Mild shock applied to it may cause the material to break. The process of forging compresses the molecules inside the alloy, which results in a denser surface area compared to a cast piston.

It is true that forged pistons are heavier than cast pistons, but this is counteracted by the ability to provide a high compression ratio inside the engine, enabling the engine to rev higher and produce more power. Most turbocharged and high performance car models use forged pistons because they're more tolerant to the abuses of extreme heat, detonation and pressure inherent in performance oriented engines.

An engine modification tweaked toward producing more power will benefit from a forged piston, as the high tolerance to abuse enables the tuner or engine builder to make incremental adjustments to enhance engine performance. Forged pistons are also readily available compared to cast pistons which are only available in OEM sizes, hampered by the expensive casting process.

Choosing the Right Piston
A stock engine will make do with a cast piston to save on cost. Engine builders employ different theories regarding the type of piston to be used. Forged pistons are more expensive compared to conventional cast pistons, and are decidedly more durable in terms of shatter resistance when exposed to extreme temperatures inside the combustion chamber.

This does not mean that cast pistons are inadequate. In fact, they are more than enough for most applications. The car enthusiast has to analyze the different factors involved in engine modification to make the decision on what type of piston to use.

Modified/Turbocharged Engines
Ask any certified engine builder and most will agree that a high compression or turbocharged engine geared towards performance will operate better with the use of forged pistons. Custom engine builders also prefer the wide variety of customizable designs that a forged piston provides. This allows them to suit the shape of the piston with the kind of performance benefit they want to achieve. This also makes it easy to properly tune and enhance engine tolerance during testing and actual use.

Modified or turbocharged engines are subject to higher amounts of mechanical stress and have to rely on durable parts designed specifically for extreme amounts of abuse. Using forged pistons in the engine setup will definitely yield performance points that will suit any preferred modification on the engine.

Stock and mildly tuned motors do well with traditional stock cast pistons and present no disadvantage in terms of power and performance. It would be best to consult a professional mechanic or engine builder regarding engine modifications and performance enhancement.

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