How is the flex plate balanced?

[Jeff65]

What niels is saying is there is "factory balancing" which is good enough for the rpm range of the factory vehicle. Then again there is "performance balancing" which is an extra effort made in a precision machine shop to carefully match components to eke out the best possible performance. Factory balance is good to about 6000 rpm redline. If you intend to push the engine to the limits, say 8000+ rpm then you need the extra effort of precision balancing. There is often very little difference between the two, but if winning is your goal, every little bit counts!