Automotive torque specifications indicate the torque necessary to correctly stretch a bolt or stud. These specifications are determined by vehicle manufacturers and recorded in their service manuals.
Bolts and studs need to be stretched an appropriate amount in order to successfully hold the parts of the engine together. The preferred tool to meet torque specifications is a torque wrench. Stretching the bolt often requires 30W engine oil, and specialty fasteners may require a different type of lubricant. To achieve the manufacturer-recommended torque specification, the right type of lubricant must be used, as lubricating the threads of a bolt allows it to be turned further than it turns when dry.
There are two methods for tightening bolts to achieve the proper torque specifications. The torque plus angle method applies a consistent stretch to all of the bolts. Perform this method by seating the bolt with a torque wrench and turning it the recommended amount of rotations. After rotating, measure with a torque angle tool in order to complete the turn by the number of degrees the manufacturer suggests.
The torque-to-yield method involves fasteners that are stretched almost to their limit and are intended for one use. This method is most commonly used on cylinder-head bolts.