The most common type of steel used for high-performance connecting rods is 4340 chromoly steel. 4340 has a tensile strength of 145,000 psi. Its hardness, ductility and other properties will vary based on the heat treatment applied to it. 4340 may also be referred to as aircraft grade or aircraft quality steel.
The crankshaft, connecting rods and bearings are extremely important in every engine build, whether mild or wild, because they convert the reciprocating motion of the pistons into rotational torque. The longer the stroke, the greater the leverage effect and the greater the torque output of the engine. There are three things that need to be considered when replacing a crank, rods and bearings:
Billet connecting rods are built from a single piece of flat forged steel. They are designed using a CAD-type computer program, then individually cut from a billet material using a water jet or other CNC-controlled machine.
It is imperative that you pay attention to the connecting rod bolts when you purchase and install your new connecting rods. These bolts are the single highest-stressed fastener in your engine, according to Davis.