Maybe this will help you understand, Look at the bolts pictured . The top of the bolt keeps the shank centered in the hole which allows space to be spread evenly around the bolt for the oil to travel. This insures the bolt shank not to move against the smaller drilled oil feed hole in the top of the head when torquing it.
Common ARP Studs do not have this under cut in the shank. They are the same exact diameter as the hole which leaves no room for oil to travel. Can you drill the head? Yes, Go ahead be my guest. And who is to say the stud stays in the center at the top of the hole after torqued with no taper to keep it centered.
You all can drill the head hole larger. We'll keep doing what we do for over 30 years with no issues. Using the proper bolt or Modifying the 2 studs.
And as far as the Call to ARP. I say Bullshit! My son talks to them weekly he is a dealer for them and places orders every week. We discussed this with them at great detail on how much could be removed without compromising the tensile strength torque value recommended for this application . It took over #125 lbs without any failure far exceeding the torque needed. They are also used over when the engines are refreshed for the new race season and still torque just fine.
When doing this mod don't grind it in . It must be cut uniform and no uneven edges rough edges.
Last picture they do make and sell under cut studs. There is one pictured with standard studs. Very expensive. 4 times the amount then standard thread rolled heat treated studs.
The $100 a set is what we are paying for the stud kit. To have the 2 studs modified it is around $25 a pair for engines built here.
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