Your question/answer doesn't make sense. If your bow remains at the same weight and draw length your arrow will not increase KE...ever unless extremes are taken.

A bow has X amount of KE....going to a heavier arrow will slow your bow down however the KE will remain relatively exactly the same. Going to a lighter arrow will increase the speed of the bow but again, the arrow will retain relatively exactly the same KE. Your trading weight for speed but not for KE.

The only way KE will change is if you go to a heavier arrow and increase either draw weight or length.

I'm refering to relatively the same KE ie within a ftlb or 2 or less but not enough to be that concerned.