Ah, memories. It seems like only yesterday when offset grinding a crank for a miniscule bump in cubic inches was the only game in town. Anyone lucky enough to score a 400 small-block crank at a swap meet stashed it away in a safety deposit box. My oh my how times have changed, because unless your Mouse packs 427 cubes these days, forget about getting any respect on cruise night. Even a 540 is merely a modestly sized big-block by today’s standards. You can thank the influx of affordable aftermarket stroker crankshafts, and the market is changing rapidly. While the first wave of affordable cranks inundated the market with tons of stroke lengths for a variety of applications, the focus has shifted since then. Now every new generation of cranks brings improvements in finish machining, heat-treating, mass reduction, oiling, and ease of balancing. To get educated on the latest developments in crank and rod technology, we hit up Shane Pochon of Lunati. The company has been churning out premium quality rotating assemblies for decades, and has recently revamped its product line. Additionally, we asked Shane to delve into some more general crank and rod basics, covering everything from metallurgy to manufacturing techniques to harmonics.
In recent months, Lunati has completely revamped its lineup of crankshafts. Our entry-level Voodoo crank offers high-quality features at a budget-friendly price. These non-twist 4340 steel forgings are nitrided for extra durability, and have micro-polished bearing surfaces for reduced friction and wear. Although they’re priced for budget-conscious engine builders, our Voodoo cranks boast high-end features like drilled crankpin arms to reduce rotating weight. These cranks will handle up to 1,000 hp, making them perfect for street and mild race applications. Lunati’s Signature Series cranks offer many of the same basic features as our Voodoo cranks, but with more bells and whistles. While they’re also forged from 4340 steel, the Signature Series crankshafts are manufactured from the highest-quality aircraft-grade material in terms of cleanliness and purity. These American-made cranks feature gun-drilled main journals, profiled counterweights, and a deep-drilled crank snout to better support balancers and blower pulleys. While that doesn’t make much of a difference in power output, Lunati’s Signature Series crankshafts have proven reliable in engine applications exceeding 1,500 hp.
Cast vs. Forged vs. Billet
Crankshafts can be of cast, forged, and billet construction. A cast crankshaft is the most basic and inexpensive. When making a cast crank, metal is poured into a mold, which results in a casting that very closely resembles the shape of a finished crank. This reduces the labor required to machine the crank into its final shape, in turn reducing costs. Cast cranks often use the cheapest raw material as well. The drawback of this approach is that with a casting, the grain structure of the metal runs all over the place. In contrast, forged cranks start with higher quality material, and the forging process involves compressing the metal into shape in a die. By compressing the metal, the grain structure gets rearranged and strengthens the crank. Just like wood, the metal used to manufacture a crankshaft has a distinct grain structure. With a forging, the grain structure is aligned parallel like wood, which helps hold the crankshaft together.