Did you mean that the studs were torqued down to 18? Or did you really only torque them to 8?
I torqued the studs to 8 lbs. Going off these instructions:
1. Long threaded end must be installed in the case.
2. Note stock stud length location before removing. There are two different stud lengths.
3. After removal of stock studs (removal tool #SP-100 available from APE) thoroughly clean holes with solvent and blow out.
4. Use APE stud installation tool #08-151 or two 8x1.25mm nuts on the noted location, bottoming out, then using a torque wrench torque to 8 ft. lbs. maximum.
5. Install head, and following manufacturer's torque pattern, torque nuts to 20-22 ft. lbs.