First off i will say i'am a big fan of ARP products. But i had a engine fail in the weekend that was partly caused by the arp head studs. I found that both camshafts had starved of oil. After pulling the head and checking the oil flow/pressure coming out of the block to the head, i found the problem. The oil feeds up the side of the bolt into a oil galley 1/2 way up the bolt hole and thats how the cams are feed. After checking the hole for the head stud against the toyota factory bolt and then the ARP head stud i found the problem.
the toyota bolt is 8.41mm thick
the ARP head stud is 10.00 thick
and the hole for the head stud is only 10.80mm wide.
So that means there is only a .40mm gap for the oil to flow into the oil gallery. My fix for this is to machine a 3-5mm groove up the bolt hole to the oil gallery.
I hope this article helps someone out as i'am up for 2 new cams and 3 months of porting and about $900 of machine work again. i dont wish that on anyone.