Most commonly used in automobile engines, connecting rods are generally used in an internal combustion engine. The connecting rods link the pistons to the crankshaft and provide fluid movement between them. Farm equipment, cars and truck, construction equipment and any other type of vehicle with an internal combustion engines uses some type of connecting rod.
Connecting rods are typed by the process used to manufacture the rods. The process of making forged connecting rods constitutes forcing the grain of the selected material, such as a steel alloy, in the specified shape of the rod. Manufacturers use different types of steel alloys including 4340 steel or a chrome and nickel alloy. The nickel/chrome alloy increases the strength of the connecting rod without making the finished product brittle.
Cast rods are generally the choice of original equipment manufacturers because they handle the load of a stock engine and are less expensive to make. Cast connecting rods possess a seam down the middle that is noticeable and differentiates it from the forged type. Do not use cast rods in high horsepower applications over 450 and going 6,000 rpm.
Another original equipment manufacturers choice is the powdered metal connecting rod. A powdered mix of metal is pressed into a mold and heated at high temperatures to melt the mixture into a solid form. Little machining is necessary with the powdered metal rods because they come out of the mold basically a finished product. These rods are less expensive to manufacture than steel and stronger than cast connecting rods.
Billet connecting rods are the ones that are generally used for high-end racing vehicles. Billet rods are machined from one piece of steel or aluminum and are lighter, stronger and more durable than other types. Some billet rods are specially designed with features that reduce stress risers and ease into the billet material's natural grain.