DI TECH
readily support reduced skirt area designs via
appropriate machining to minimize friction
and weight.
Machining operations for forged and billet
pistons occur on the same equipment. In the case
of forgings, the under-crown structure is created
with smooth transitions to the pin bosses and
supporting structures by the forging die. On a
billet piston, the under-crown must be fully ma-
chined, where it is optional on a forging. Forgings
may enjoy smoother transitions between the pin
towers and the under crown because the tooling
On a forged piston such as this Diamond LS2K, under-
crown milling is a feature designed to improve crown
thickness uniformity and reduce unnecessary weight.
On a billet piston, under=crown milling is required as a
means of creating the piston shape.
forces it. Billet machining operations can often
approach the smooth transitions found in forg-
ings, through precise CNC programming.
Billet Applications
NHRA Pro Stock teams and NASCAR cup
teams were among the earliest proponents of
billet pistons, quickly grasping the potential to
re-evaluate component relationships between the
piston, combustion chamber and valve angles for
maximum power and efficiency. Diamond Pistons
was one of the earliest manufacturers to embrace
the billet movement, but it quickly discovered
the challenges of folding it into everyday pis-
ton manufacturing. So, it developed a dedicated
department with its own engineering staff and
equipment to meet the varied and specialized
requirements of billet production.
This billet piston started out as a solid puck of
aluminum. Note the shirt profile, struts, and all of
the other material that had to be machined away to
yield such a complicated shape. Despite the added
machining complexity, a billet piston can be created
quicker than a from-scratch forging because it does
not require the creation of a forging die.
While forgings are the bread and butter of most
race and performance applications, billet pistons
are often the choice of race shops and race teams
that highly customize their pistons. Diamond’s
rapid turnaround time, due to their expertise
and investment in billet technology, helps teams
experiment with different piston designs to opti-
mize their racing programs. Billet pistons make
it possible to quickly design, test, and evaluate
new ideas. -JOHN BAECHTEL
Once the piston is finished being machined, it is often
difficult to distinguish a forging form a billet. However,
in terms of ultimate strength, forged pistons do have a
slight lead because of their favorable grain structure.
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