If done any idea how much HP it will free up? and What are the pros and cons?

 

not worth the amount of money it costs.

 

cost... for a good internal balance job.... few grand.

i don't think you're going to get much in the way of horsepower out of it. most of this kinda work is done on cranks that have been either cold or shot hardened for racing use and are then super well balanced to handle crazy high RPM. unless you're building a legit race car engine, i'd leave it alone.

 

not worth it..the bottom end can already handle high rpm. it would be worth it more to leave the bottom end alone and build a really good head. Unless like stated you plan to build a extended period high rpm race engine.