Manley Performance‘s newest round of small-block Chevrolet crankshafts includes a 4-inch stroke, two-piece rear-seal crank for the venerable Gen I small-block Chevy engines. Manley’s Bob Schmalz showed us around the new piece.

These cranks are forged from 4340-alloy steel, a very strong alloy that is well-known for its toughness. Heat treating 4340 steel greatly enhances the strength of a crankshaft. Manley chooses the Nitriding process to heat treat most of its crankshafts.

Nitriding is where ionized nitrogen is vacuum deposited onto the crankshaft’s surface while in an oven. The nitrogen penetrates the surface of the steel, changing the microstructure of the material. The surface hardness in increased dramatically. Manley’s new crankshafts are heat-treated, and stress-relieved by shot peening. The units are Magnaflux tested for quality control.

The cranks have large-radius journals, and narrowed rod-bearings are required. The journals are micro-polished to ensure smooth operation and a long life. These cranks have a lightweight, internal-balance design.

Like many of Manley’s other performance forged crankshafts, these are a non-twist forging. Because the non-twist forging is manufactured with all four throws being forged simultaneously, the internal crankshaft stresses are reduced during the manufacturing process.

The 4-inch stroke SBC crankshaft (Part #190130) is designed to be used with a 6-inch connecting rod, and has the standard Gen I main-journal diameter (2.450-inch) and connecting rod-journal diameter (2.100-inch). The crank weighs-in between 49 and 51 pounds.

For more information on this crankshaft or other Manley Performance Products, visit them online at Manley Performance.