What Are The Differences Between Billet And Forged Car Parts?

Billet and forged car parts have the same starting point: a processed piece of metal. But what happens to that metal afterward is different, and that gives their resulting components different traits, too. At the most basic, billet components — created by machining the metal — can be made to more precise specifications. Forged parts, where the metal is physically formed into shape, usually after it's been heated, are stronger. 

Now, regular Jalopnik readers may also remember when we looked at the difference between cast and forged crankshafts, which was about making car parts with two of the earliest metal-shaping technologies. People began casting metal — heating it until liquid then pouring it into a mold to harden – approximately 6,000 years ago. And forging may have been around even longer.

It took until the early 1970s, however, for billet manufacturing to really make an impact on the auto industry. That's when the late John Buttera, a legend of the hot rod world, was working on a 1926 Model T and opted to make his own billet wheels and suspension components for the car. (In fact, he's considered the outright inventor of the former.) In both cases, though, it meant taking a solid piece of metal, essentially a specific type of forging blank called a billet, and using a CNC milling machine to precisely remove unwanted material, leaving behind a finished part. True, "CNC" stands for "computer numerical control," and some might say it was that factor — the computerized automation of machining — that enabled a practical way to make billet parts. Yet Buttera remains the father of billet components for generations of gearheads.

To understand the strength advantage of forged parts, you have to know a little about metallurgy as well. Generally speaking, metals used for car parts are made of microscopic crystals called grains, and the size and orientation are what give metal its strength. Metal parts made with smaller grains that are aligned in the same direction tend to be stronger than when the reverse is the case. It's also worth emphasizing that because a billet is the same as a forging blank, parts made from both start with the same grain size and alignment, which is usually pretty random.

Now, the forging process breaks down the grains in the blank into smaller sizes and forces them into alignment. Machining, on the other hand, can break the flow of grains as the metal is cut, making the metal weaker. When parts have to be made into complicated shapes and/or meet extremely tight tolerances — like if you're crafting a billet aluminum center console for the $4-Million, 1,800-hp Bugatti Tourbillon – a CNC machine with a laser cutter offers the most precision.

We can also take this into the speed shop for a real-world scenario. Say you want to fine-tune the shape of a piston head to improve combustion: using a CNC machine to remove a few millimeters of metal from the original piston design would be much quicker and simpler than having to re-forge an entirely new part. Alternatively, because some high-performance cars need forged pistons for their added strength, folks can use billet machining to save time and money on prototypes and then rely on forging for the final parts.