A little while back I noticed a loud rapid fire noise when on the loud pedal, and not a good noise.  It didn't take long to work out that I was the newest victim of Porsche's experiment into exotic metallurgy.   The Dilivar steel exhaust studs on 2 cylinders had snapped!   This is becoming an all too common thing on aluminium block 911's.  I decided to fix it now instead of waiting for more to let go and do further damage.   After a lot of research and talking with people whom I trust on the s