I'm not sure about the exact sizing though... maybe someone here knows. But I do think the last little bit of piping before connecting to the rear part is 3'' on both midpipes... am I correct? Is the beginning of the rear part 3''? If so, and if both midpipes end in a 3'' pipe, then the restriction to flow will be the rear part anyway... even if midpipes were 4 or 5''.. to say something. Am I still correct?