vector1 100 psi with 100 and 120 psi gauges are the correct way to check for compression. I have done FE heads checking for porosity with 75 psi and had no problem. Check the pressure to 100 and out comes the leak. This was in a combustion chamber. The first time the motor would have run, the head would have cracked open like a water melon. If you are retoqueing head bolts or studs, you shouldn't back off them to 0 and then crank them down to spec. Your leak may have stopped because you are crushing the gasket tighter after a couple of heat cycles. Some gaskets are OK with your idea and some will just blow out. Did you
oil the bolts or studs before the retorque?This will effect the final number also. I hope that just the bolts or nuts where low on the head torque spec. When you are doing the retorque follow the procedure for starting in the middle and working out on both sides. If you start at 1 end and work across the head you can pinch the gasket on the started side and not have a good seal on the other end. Your problem may only have happened when the motor was cooling off. Are the heads Aluminum and the block iron?? There is an expansion issue with these 2 metals of about .0012-.0015". Good luck and watch the
oil for cream and the breathers in the valve cover. Make sure the valve cover has NO pudding in it. If it does, you have washed the bearings. Change the
oil and filter a couple of times and watch the oil pressure on a cruise. Rick L.