Cylinder Pressure

More advertised duration,usually needs more physical compression (milled heads/flat top pistons,etc). Split pattern cams,bleed off duration to a degree as well. RRR's definition,nails it dead on. If that intake valve hangs open longer,cylinder pressure drops by that valve hanging open .10 degrees is a HUGE difference here. You bump the mechanical compression up,to compensate. It's a fine line of balancing it here.