Just finished this build.

Stock untouched manifolds. "Mild" FAST build.

596 HP. 607 lb/ft trq.

Point is EH is a surface preparation. It does nothing in the way of "hogging out". Little of the parent metal is removed. And after a short time of run in, the manifold gets a coating of surface rust and carbon buildup, so any gains in surface prep quickly vanish. Then add to that fact that you still need to run it through a stcck type 2.5" exhaust system. Better than nothing. perhaps, but don't expect much.,,,