The term “billet” generally refers to components which are machined from a drawn or forged blank of aluminum, usually 6061 alloy, rather than a cast shape. Billet aluminum differs from cast aluminum both in alloy and grain structure. The 6061 blank has a highly uniform and dense molecular structure which results in an extremely strong and stable component after it is machined and heat treated. Billet engine blocks have much higher elongation properties than cast pieces, making them far more resistant to cracking when subjected to the extreme stress loads encountered in racing engines.
Billet also allows the design of the block to encompass features which are not available in a casting. Because it is completely machined from a solid cube, bore centers, deck height, cam location, bolt patterns and other features can be altered almost without limitation. This technology has enabled engine builders to create a new generation of racing power-plants which defy the imagination in terms of their size and sophistication.