ARP started applying technology to race fastener design and manufacturing in 1968.
Today's critical fasteners - head studs and bolts, main studs and bolts, and driveline - have been designed stronger than ever before to handle the extreme loads. As a results, installation pre-loads - the amount the fastener is stretched during installation - are very high.
There are three methods that can be employed to determine how much tension is exerted on a fastener; using a torque wrench, measuring the amount of stretch, and turning the fastener a pre-determined amount (torque angle). Of these methods, use of a stretch gauge is the most accurate.
The following material is intended to provide a brief overview of the metallurgical considerations that influence the design and production of the most reliable fasteners in motorsports. It is hoped that a simple understanding of the knowledge and commitment required to produce this reliability will make your future fastener decisions much, much easier.
The materials ARP uses in fastener manufacturing are listed and compared.
There are six types of metallurgical failures that affect fasteners. Each type has unique identifying physical characteristics. The following examples are designed to be used like a spark plug reading chart to help analyze fastener failures.
