High Tensile 6.9 IDI Head Stud Kit
There are After years of development we finally have a modern performance head stud option for our 6.9 IDI owners, this high tensile head stud kit is centerless ground, heat treated prior to thread rolling and machining, and are nominally rated for over 220,000 psi tensile strength, which is by far the highest tensile rating of any 6.9 head stud kit on the market.
The commonly used but now outdated ARP 6.9 head stud kit uses a cheaper, 8740 grade material, with a torque spec of only 80ft lbs, which being only 5 ft lbs more than the stock head bolt torque spec, is not a significant upgrade. This new high tensile kit comes with a torque spec of 125 ft lbs, which is equivalent to the ARP 1/2" 7.3 fastener spec despite being only a 7/16" fastener, with the ability to be overtorqued into the 140-150 ft lbs range, where the old 6.9 ARP kits would often fail around 100-110 ft lbs.
ARP Material Guide: https://arp-bolts.com/p/technical.php
"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."
