Yeah, I initially wrote this up for RKO I believe, but I usually cross post info like this on all the boards I'm on. It was before I was on here though.
To sum up what I said above, we can't measure bolt stretch or clamping force, so we have to use torque applied. Anything that changes that will change the clamping pressure. Since fasteners like ARPs are usually supposed to be used at about 90 percent of thier tensile strength, being off 10% in either direction can be bad, for obvious reasons.
An example is a chunk of dirt or rust in the threads, you torque it to the 90 ft-lbs, then after a few hot-cold cycles (expansion/contraction) that piece of rust is pulverized into a powder. Now the stud is loose
Plus it would have created friction in the threads, which was gone over above.
So yeah, its very important to be sure those threads are clean. I lost a couple HGs right in a row at relatively low power (16g, 35-40 lbs/min), then went to running as much as 64 lbs/min without losing a single gasket in a couple years. The combination of ARP moly lube and proper preperation for the studs is all that I changed