dont forget you got 2 tail pipes so tech your going from 2 1/2" to 4" if you catch my drift on the old one,
the new one is going from 2 1/2 or 3" depending wat they fitted to a 5 or 6" exit combined on the tails,
the guy a powerflow who im my eyes is one glever sod sat and workrd out the distance from the front of the car to the rear, the size of the silencers the size of the pipe and said that i needed 2" pipe to feed the tail pipes so i did not loose any back pressure if i loose the back box,