what am i going to expect if i change the limbs on my black widow pma2.they are the same weight,except the new limbs are 4 inches longer.will my nocking point change and will there be any performanc lost,will my brace height be the same...in other words someone walk me through what you do when you change limbs

You will need a new string and re set the nocking point. Your brace height will increase-1/4 to 1/2 inch. You will need to retune your arrows and find the new brace height-let the bow tell you. You may get an increase in performance-longer limbs store more energy.

Bjorn got it right.  In addition, I think you are going to find the bow feels smoother on the draw and your shooting may actually improve.  Longer limbs (for me at least) are more forgiving of the small form errors most of us have.