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To further clarify the issue (if that is even possible :))
the rotors must be dynamically balanced about their own
axis as well as exactly match a precise weight target.
It is not sufficient if they merely weigh the same.
If they are anything other than the exact weight they
will not perform  properly in the over all balancing of the
engine as the counter weights are counting on them being
in perfect dynamic balance and be of the correct weight.
Pardon the pun.

Furthermore if the rotors them selves are not in dynamic balance
they will have a detrimental effect on the rotor bearings.
One side and end of the bearing will wear more than the opposite
side and end. In other words the rotors should be mounted on a
special shaft and spun up to check their dynamic balance.

-- 
Paul Lamar ...No rotor no motor.

Confusing eh?
Yep, the rotors are dynamically balanced at the factory.  The circular
machined
depressions in the side of the rotors near the apex seals are for that
purpose.
Cheers
Cary

I think they have done away with that on the RX8 rotors as they consider
them much much better as cast. I could be wrong but of all the RX8
rotors I have seen so far pockets like that are not evident.