Stock rod bolts are stamped 12.9 on the head. 12 is the ultimate tensile strength in hundreds of MPa, .9 multiplied times the ultimate is the yield strength in hundreds of MPa. So the stock bolt has an ultimate strength of 1200MPa and a yield strength of approx. 1100MPa. This works out to approx 177000psi and 160000psi in english units. ARP 2000 material is stated to have an ultimate strength of 220000psi, no yield strength is listed but typicaly .9 X ultimate would be close giving 198000psi. The factory stresses the stock bolts beyond the yield point (stretched or plastic deformation) this puts the installed stress at some point over 160000psi I dont know the exact number but I will estimate at 168000psi. ARP bolts are not plastically deformed when installed so the installed stress is less than 198000psi I will estimate 185000psi. This increase in stress results in an increase in clamping load of 10 percent if the smallest bolt cross sections are the same. This is not a very large increase. The greatest advantage of ARP bolts in my estimation is an increase in fatigue resistance of the material and possibly better quality control.
