yong,
These kinda things are trial and error... if ur engine has been sent for full balancing before, then most likely there won't be any problem... if not, scared is that there's manufacturing inbalance; engines are being mass produced, there are bound to be slightly flawed... obviously all these has already been taken into account and calculated to give optimum reliability, therefore rev cut has been set to 6800 rpm.
lampakia,
Changing engine internals... doesn't necessarily need engine blue printing lar... so expensive... unless u're trying to build a race car maybe lar... other than that, just send the engine for balancing can liauz... balancing itself also will cost over 1000, engine blue printing i dun dare to even ask how much will it be..!!! Wahaha... a couple thousand bucks maybe...
boyzone,
I don't have an answer for u... but just to comment on Q1, these kinda things are subjective... nobody can give u an accurate answer as different engines, with different mods, and under different conditions... will give different FC... I not carbie pro, so sorry... can't find an answer for u... =Þ Maybe ayell can answer?