Manley’s H-beam connecting rods are formed from billet 4340 steel. 4340 steel is a heat treatable, low alloy steel containing nickel, chromium and molybdenum. It is known for its toughness and high strength in the heat treated condition while retaining good fatigue strength. It is used for applications such as aircraft landing gear, power transmission gears and shafts, connecting rods, and other structural parts. The rods are shot peened for even more strength. Shot peening is a cold working process that produces a compressive residual stress layer and modifies the mechanical properties of the rods. It entails impacting a surface with shot (round metallic, glass or ceramic particles) with force sufficient to create plastic deformation essentially cold working the surface. Shot peening can increase fatigue life by up to 1000%. The materials and processing are closely monitored for optimum performance.
The rods are designed and finish honed in the USA with sizes held to some of the tightest tolerances in the industry, +/- .0001” and +/- 1 gram per end. This important aspect is a must for a balanced rotating assembly. The Manley H-beam connecting rods also exclusively use ARP 2000 fasteners. From ARP’s site on ARP 2000 fasteners, “ARP2000 is a heavily alloyed martensitic quench and temper steel, initially developed for use in steam power plants. As such it has excellent stability at high temperatures. But most important, ARP research discovered that in addition to temperature stability it has excellent notch toughness in the higher strength ranges and is alloyed to be tempered to Rc44/47. 8740 and 4340 can be tempered to the same hardness. But, the tempering temperature would yield material in the “temper brittle zone” (between 500° and 700°F), producing significant notch sensitivity. ARP2000 is tempered above that temperature range and has a strength between 200 and 220 Ksi.