Forged is always better if the forging is available. That's the problem: availability. Due to tooling and therefore cost, forgings are typically only for large production runs. Billet material is used for low production numbers.
Here's the difference. Steel starts out as an ingot (a cast block). While hot it is rolled to the desired thickness, making a billet. The billet is much more resistant to cracking across it's length because the rolling has imparted a directional grain to the metal. Picture a 6" x 6" x 36" piece of wood, it's kind of like that. If you machined something shaped like a crankshaft from this piece of wood, bridged it between two chairs and stood in the middle, what would happen? It will most likely break through a section of exposed endgrain.
A forging starts with a billet. The tooling involved is a heavy press that will form the billet to the desired shape before machining. Picture the hot metal as a bundle of cooked spighetti pressed in a waffle iron and allowed to harden (Kids, please don't try this at home). Now when the part is machined the grain is following the shape of the part and is much less prone to failure.
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1988 GT, 5-speed, white, beechwood leather, 3.4 DOHC installation in process.
[This message has been edited by sspeedstreet (edited 06-02-2005).]
A billet is simply a solid piece of material that is shaped into it's finished form by machining. Most finished products are either cast or molded into shape. A billet is a raw block of material.
