The crankshaft is, by far, the most massive moving part in your race engine. There's a reason for that-the crankshaft is essentially ground zero for every bit of the torque your high-buck race engine is capable of producing. It's eight pistons connected to connecting rods, which in turn are connected to the crankshaft, pounding down intermittently with incredible force. Meanwhile, at the back, the crank is connected to the clutch-and eventually the rear wheels-which is trying to resist acceleration. The same thing is going on at the front where the water pump, alternator, and other power-robbing assemblies are providing resistance
The result is a multitude of twisting forces applied to the crankshaft the entire time the engine is running. The stresses are multiplied in a racing situation in which the rpm levels can get quite extreme, and the frequent transitions from wide-open throttle to zero throttle only add to the equation.
Fortunately, these thoughts are nothing new to racing engine builders or the companies that supply them with aftermarket crankshafts. Because of its expense and the trouble involved when one breaks, racers require the crankshaft to be dependable-virtually bulletproof. But because excess weight limits maximum rpm, the lightest crankshaft possible is also desirable. This means that a stock, cast crank is suitable only for the most entry-level, cost-conscious levels of racing.
Forged vs. Billet
Crankshafts that are purpose-built for oval track racing are almost exclusively either forged or constructed from a piece of billet steel. Both offer supplemental strength over cast pieces in addition to other advantages. Forged pieces are relatively inexpensive. Forgings produce a stronger grain structure and, if fully machined, can be exceptionally strong. Advancing CNC technology allows for billet crankshafts with extreme precision. A solid piece of steel means great continuity and allows a more consistent heat treat after the cutting is complete. Also, because each crank is cut individually, a piece with really unique specs can often be cut from billet more cheaply than forged.
Either way, a quality crankshaft that's either forged or billet is ideal for medium- to high-horsepower racing engines. Ultrahigh-horsepower engines usually use billet pieces, but one engine builder told us that for medium-horsepower engines, his decision between forged and billet cranks usually comes down to availability.
The Crankshaft Diet OEM
Crankshafts are designed to last well over 100,000 miles and to operate for extended periods at low rpm levels. While the big three might be hesitant to admit it for certain models, maximum acceleration is actually pretty low on the priority list.
For racing, however, acceleration is paramount, and every extra pound of crankshaft the engine has to spin is just that much more power that's robbed from the rear wheels. First, the crank can be gun-drilled, which is essentially hollowing out all the main journals. Rick King, owner of King's Crankshafts, says this can cut as much as 3 pounds out of the crank, but because it's in the very center of the rotation, the gain is minimal. The same thing can be done to the rod journals, which will shave a couple of additional pounds