9/16 Head Studs

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Thread: 9/16 Head Studs

  1. #1

    Default 9/16 Head Studs

    Thoughts? I know there has been a multitude of discussion on head sealing, especially on bigger bore aluminum motors, but I don't think I have ever seen larger studs mentioned, even though it is somewhat common in the aftermarket/racing world.

    Last edited by rainyp71; 04-14-2019 at 06:03 PM.

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  3. #2


    The 9/16 and ⅝ inch head studs are primarily a fixture from the blown alcohol and nitro classes, Robert. Our OEM head stud diameter of 11mm is essentially 7/16 in SAE speak. While there is likely adequate material in the casting to go to a ½ inch head stud, going larger gets progressively more risky on two different fronts.

    The first front is the amount of material around the stud anchor point. Each time we go up in stud diameter we reduce the total amount of material anchoring the stud. One step up from 7/16 to ½ probably doesn't matter. Above that the ice starts getting thin and so does the block material. The second front is the inherent strength of the casting. ARP2000 1mm studs begin to crack the block at 115 ft/lbs of torque. The stud seems to be OK but the block is not. Bigger studs load the casting more heavily which brings us back to the first front issue.

    In the FWIW column, Accufab offers a step stud that has a 9/16 coarse thread on the block side and a ½ fine thread on the nut end of the stud. Predicatably you will have to do a little machining to se the studs but there is a ready made package if you wish to experiment.

    The other path that might be worth exploring is to ask ARP to make some 11mm studs out of their 625 steel which is an even larger improvement over 2000 steel than 2000 steel is over 8740 steel.


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