On mine I just cut and ground back on some 90 degree bends as in the 'photo. The "slot" produced was a 6" x 3" oval (maximum points), I figured that was enough area for a dual 4" system. I've also seen them where they are just a pure "X" with 90degree intersects. It's steel and now painted black, I plan to do it in stainless eventually. We didn't pick up anything over open headers but we didn't lose anything either. It also made the car quieter, levels went from 124.5 db to 120.1 over open headers. We have a 120db limit at the track. HTH's