Clamping force: is less with the arp's because they don't flex and oem do.
I would assume that
clamping force (that is, the linear force down the length of the bolt) is higher because that's generally the point of going to aftermarket head studs: to keep the heads from lifting under increased cylinder pressure.
The
rotational torque may be less, or not -- hard to say since they use different tightening techniques. You'd need to either measure how much torque it takes for new OEM head bolts to each 30 lbs-ft + 120 degrees + 90 degrees, or how many degrees degrees past 30 lbs-ft the ARP studs take to hit 90 lbs-ft.
If the ARP studs are stronger, it may take less stretch to achieve the same clamping force, but it also probably takes more rotational torque to achieve a given stretch, so you could end up around the same place.
So if I put any torque on the studs threads that thread in to the block that will be add more force to block threads when I tighten the head down. And then risk ripping threads out of the block.
Aside from aftermarket fasteners being designed to a higher strength in general, one of the things that tends to make studs better than bolts is that the bolt will only be partially threaded as you tighten it, while the stud starts out fully threaded (as does the nut up top), so you always have full thread engagement as you tension the bolt.
Since the stud is free to rotate within the head, and typically comes with lubrication, my assumption is that torque is applied more or less evenly between the threads in the block and those in the nut. If you were to torque the stud into the block, and then torque down the nut, my *guess* is the block-side threads wouldn't see much additional torque until the nut-side approached the torque the block was already under, ie your pre-torquing would be more unnecessary than catastrophic, but I certainly wouldn't risk my threads finding out
Maybe someone more well-versed with the mechanics of fasteners can chime in...
