When you increase the power on your engine, you must upgrade the hardware holding down the head to prevent the head from lifting under high cylinder pressure. This is a recommended upgrade when you upgrade the head gasket to run ore boost on a 2JZ engine. These are a stronger upgrade over the factory head bolts that are one time use yield stretched bolts. This is a recommended upgrade for running up to around 35psi boost max. Upgrade to ARP Custom Age 625+ for even higher clamping force.
8740 Chrome Moly: Until the development of today’s modern alloys, chrome moly was popularly considered a high strength material. Now viewed as only moderate strength, 8740 chrome moly is seen as a good tough steel, with adequate fatigue properties for most racing applications, but only if the threads are rolled after heat-treatment, as is the standard ARP production practice. Typically, chrome moly is classified as a quench and temper steel, that can be heat-treated to deliver tensile strengths between 180,000 and 210,000 psi.
