Forged or Cast Crankshaft?
A forged crankshaft is recommended for all power adder and high rpm race applications, although a cast steel crank can tolerate some moderate race applications including some limited boost and nitrous use.
How to tell if it's a Forged Crank
Many engines were produced with both forged-steel and cast cranks over their production lives. It's surprising how many of us have a hard time telling a forged crank from a cast crank while looking right at them. It's easy to tell them apart, if you know what to look for. Here are some quick clues:
The casting process results in greater control of the net shape in the forming process, which is evident from visual clues in the finished crankshaft. Looking at the counterweights is a dead giveaway. A forged crank's counterweights will generally have a rougher look with rounded edges, while a cast crank by comparison will show sharp, well-defined edges.
A second visual check can be made by viewing the parting line that defines where the casting core or forging dies separated. A cast crank will have a thin, sharp, and straight parting line, while the parting line on a forging will be wide and generally less defined.
For the visually challenged, a forged crank can be identified by ear. A forging will ring like a bell when tapped on the counterweight with a steel hammer, while a casting will give a dull thud.
In addition to cast or forged, material quality also separates the different grades of crankshafts. What we're interested in is raw strength and durability. Various steels and irons are rated on the basis of strength, toughness, and ductility.
Better materials mean higher strength. Among small-block cranks, a cast iron crank may be fine for a mild performance build, but you'd be pressing your luck if big power is part of the plan. A forged 4340 steel crank will handle about as much power as your parts list can muster. Budget racers often push a crank's limits. When it comes to speed, it's a matter of how much you want to spend versus how much you want to push your luck.