Too much compression for the nitro content equals pitting in the cylinder head and piston! Not a good thing!! It also makes the engine run "less than perfect"
, as you are experiencing; the timing and compression is set up to run 0% nitro. Anything more and you need a shim or two. Call up MVVS..they will send you some shims.
As for the head bolts working loose, I've had to tighten mine once in a while, but not like you are having to. I just check all the bolts once in a while. Vibration is my suspicion; is your prop balanced WELL, not just "close enough"? When you're spinning something over 20,000 times per minute, any little imbalance is REALLY magnified. When you tighten the bolts, do as somebody metioned earlier: do a star pattern like changing a tire. After you tighten all the bolts once, go through and do it again..you will be surprised when you are able to tighten them some more!
Just curious, where do you have your pressure tap on the pipe? I was told right at the fattest section. That's where mine is and it runs great.
Good luck!
Carl